Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Pavel Machek]

Hi!

> > No, we need some kind of at least rudimentary gps framework even if we
> > allow for a raw (NMEA) interface for the time being (possibly
> > indefinitely).
> 
> Ok, that would be fine if we can get that!
> 
> For a minimal set of API I think something like this (following hci_dev) 
> would suffice:
> 
> struct gps_dev {
>   ...
>   int (*open)(struct gps_dev *gdev);
>   int (*close)(struct gps_dev *gdev);
>   int (*send)(struct gps_dev *gdev, char *data, int length);
> };
> 
> int gps_register_dev(struct gps_dev *gdev);
> void gps_unregister_dev(struct gps_dev *gdev);
> int gps_recv_nmea_chars(struct gps_dev *gdev, char *data, int length);
> 
> If that would wrap all creation of some /dev/ttyGPS0 (or however it is 
> called),
> it would fit our needs for a driver and user-space for our system.
> 
> And I would be happy to get rid of creating and registering a /dev/ttyGPS0
> in the w2sg0004 driver.

Sounds like a good start.

Best regards,
Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) 
http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Pavel Machek]

Hi!

> > No, we need some kind of at least rudimentary gps framework even if we
> > allow for a raw (NMEA) interface for the time being (possibly
> > indefinitely).
> 
> Ok, that would be fine if we can get that!
> 
> For a minimal set of API I think something like this (following hci_dev) 
> would suffice:
> 
> struct gps_dev {
>   ...
>   int (*open)(struct gps_dev *gdev);
>   int (*close)(struct gps_dev *gdev);
>   int (*send)(struct gps_dev *gdev, char *data, int length);
> };
> 
> int gps_register_dev(struct gps_dev *gdev);
> void gps_unregister_dev(struct gps_dev *gdev);
> int gps_recv_nmea_chars(struct gps_dev *gdev, char *data, int length);
> 
> If that would wrap all creation of some /dev/ttyGPS0 (or however it is 
> called),
> it would fit our needs for a driver and user-space for our system.
> 
> And I would be happy to get rid of creating and registering a /dev/ttyGPS0
> in the w2sg0004 driver.

Sounds like a good start.

Best regards,
Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) 
http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Hi Johan,

> Am 19.03.2018 um 14:54 schrieb Johan Hovold :
> 
> On Tue, Feb 27, 2018 at 08:32:50AM +0100, H. Nikolaus Schaller wrote:
>> Hi Johan,
>> 
>>> Am 27.02.2018 um 08:04 schrieb Johan Hovold :
>>> 
>>> On Mon, Feb 12, 2018 at 04:26:18PM +0100, Pavel Machek wrote:
 Hi!
 
>> Let's restart this discussion and focus on the main roadblock (others
>> are minor details which can be sorted out later).
>> 
>> If it feels like a hack, the key issue seems to me to be the choice of
>> the API to present the GPS data to user space. Right?
> 
> Or even more fundamentally, does this belong in the kernel at all?
 
 Yes, it does.
>> 
>> Thanks, Pavel for supporting our view.
>> 
>>> 
>>> But not necessarily in its current form.
>> 
>> Is this a "yes after some code fixes"?
> 
> No, we need some kind of at least rudimentary gps framework even if we
> allow for a raw (NMEA) interface for the time being (possibly
> indefinitely).

Ok, that would be fine if we can get that!

For a minimal set of API I think something like this (following hci_dev) would 
suffice:

struct gps_dev {
...
int (*open)(struct gps_dev *gdev);
int (*close)(struct gps_dev *gdev);
int (*send)(struct gps_dev *gdev, char *data, int length);
};

int gps_register_dev(struct gps_dev *gdev);
void gps_unregister_dev(struct gps_dev *gdev);
int gps_recv_nmea_chars(struct gps_dev *gdev, char *data, int length);

If that would wrap all creation of some /dev/ttyGPS0 (or however it is called),
it would fit our needs for a driver and user-space for our system.

And I would be happy to get rid of creating and registering a /dev/ttyGPS0
in the w2sg0004 driver.

Then, the driver will not need to be touched if the GPS framework is improved
in some far future (e.g. to provide some additional ioctl for getting 
kalman-filtered
position+heading by doing sensor fusion with some iio-based 
accelerometer/gyro). 

So I am looking forward to some framework for review and integration testing.

BR and thanks,
Nikolaus

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Hi Johan,

> Am 19.03.2018 um 14:54 schrieb Johan Hovold :
> 
> On Tue, Feb 27, 2018 at 08:32:50AM +0100, H. Nikolaus Schaller wrote:
>> Hi Johan,
>> 
>>> Am 27.02.2018 um 08:04 schrieb Johan Hovold :
>>> 
>>> On Mon, Feb 12, 2018 at 04:26:18PM +0100, Pavel Machek wrote:
 Hi!
 
>> Let's restart this discussion and focus on the main roadblock (others
>> are minor details which can be sorted out later).
>> 
>> If it feels like a hack, the key issue seems to me to be the choice of
>> the API to present the GPS data to user space. Right?
> 
> Or even more fundamentally, does this belong in the kernel at all?
 
 Yes, it does.
>> 
>> Thanks, Pavel for supporting our view.
>> 
>>> 
>>> But not necessarily in its current form.
>> 
>> Is this a "yes after some code fixes"?
> 
> No, we need some kind of at least rudimentary gps framework even if we
> allow for a raw (NMEA) interface for the time being (possibly
> indefinitely).

Ok, that would be fine if we can get that!

For a minimal set of API I think something like this (following hci_dev) would 
suffice:

struct gps_dev {
...
int (*open)(struct gps_dev *gdev);
int (*close)(struct gps_dev *gdev);
int (*send)(struct gps_dev *gdev, char *data, int length);
};

int gps_register_dev(struct gps_dev *gdev);
void gps_unregister_dev(struct gps_dev *gdev);
int gps_recv_nmea_chars(struct gps_dev *gdev, char *data, int length);

If that would wrap all creation of some /dev/ttyGPS0 (or however it is called),
it would fit our needs for a driver and user-space for our system.

And I would be happy to get rid of creating and registering a /dev/ttyGPS0
in the w2sg0004 driver.

Then, the driver will not need to be touched if the GPS framework is improved
in some far future (e.g. to provide some additional ioctl for getting 
kalman-filtered
position+heading by doing sensor fusion with some iio-based 
accelerometer/gyro). 

So I am looking forward to some framework for review and integration testing.

BR and thanks,
Nikolaus

Re: [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Wed, Mar 07, 2018 at 04:53:12PM +0100, H. Nikolaus Schaller wrote:

> If I look for example at the camera module drivers provided by
> drivers/media/i2c, most of them could be easily power-controlled from
> user-space by i2c-tools and 1-2 gpios through /sys/class/gpio and
> a big set of scripts.
> 
> Still they have a place in the kernel and cameras are powered on
> if the device is opened and powered down if it is closed.
> 
> So I am still trying to understand the rationale and logic (if one exists)
> behind having them in kernel but rejecting our driver which does the
> same for a different class of devices.

For media we have a framework in place; for gps we do not (yet).

Johan

Re: [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Wed, Mar 07, 2018 at 04:53:12PM +0100, H. Nikolaus Schaller wrote:

> If I look for example at the camera module drivers provided by
> drivers/media/i2c, most of them could be easily power-controlled from
> user-space by i2c-tools and 1-2 gpios through /sys/class/gpio and
> a big set of scripts.
> 
> Still they have a place in the kernel and cameras are powered on
> if the device is opened and powered down if it is closed.
> 
> So I am still trying to understand the rationale and logic (if one exists)
> behind having them in kernel but rejecting our driver which does the
> same for a different class of devices.

For media we have a framework in place; for gps we do not (yet).

Johan

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Thu, Mar 08, 2018 at 07:16:44AM +0100, Andreas Kemnade wrote:
> Hi,
> 
> On Thu, 18 Jan 2018 17:47:36 +1100
> Johan Hovold  wrote:
> 
> [...]
> > > 
> > > So to avoid having hardware information spread all over the table at least
> > > these information would need to be in devicetree. But that also all feels
> > > like a hack and hard to maintain.  
> > 
> > Having the device described in the device tree is certainly desirable,
> > not least for chip identification. And with a GPS framework in the
> > kernel with a well-defined interface, implementing power management
> > would be straight forward.
> > 
> Hmm, devicetree without in-kernel drivers, do we have anything like that
> somewhere? I thought that was a big no-go. But maybe I am wrong.

No, that's probably not a good idea, even if it may be possible (what
about ACPI then, for example?).

> > I'm just not convinced that the proposed tty interface is the right
> > interface for this. User space would still rely on gpsd for the GPS
> > protocols, and would also ultimately be managing power by killing gpsd
> > or whatever daemon that would otherwise be holding the port open.
> > 
> > Something like the generic power sequences that has been discussed
> > elsewhere might be a better fit for this if all you want to do is power
> > on and off on port open and close (and on suspend/resume). There really
> > isn't anything GPS-specific in the current proposal (besides the
> > suggested tty-device name).
> 
> So a bit like that mmc-powerseq stuff we already have?

Yeah, the generic power sequence patches were inspired by that and
intended to generalise it (e.g. to be used by the USB bus to power on
devices so that they could be enumerated). There were some issues with
that work though (which also precludes it from being used for something
like this), and it still wouldn't be sufficient to deal with the gps
device in question (which needs to monitor the incoming data).

> > But sure, that wouldn't be sufficient to deal with the
> > unknown-power-state problem with the device in question.
>
> Maybe there could be a kind of active flag set by the tty if
> there is traffic, so that active flag could be used in these
> power sequence stuff? But then again the tty layer has to be extended
> which would probably also cause a lot of ruffled feathers.

Yeah, I think this is a dead end. We need some kind of gps framework
with drivers that can implement the device specific bits.

I may have some time to look at little closer at it this week.

Johan

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Thu, Mar 08, 2018 at 07:16:44AM +0100, Andreas Kemnade wrote:
> Hi,
> 
> On Thu, 18 Jan 2018 17:47:36 +1100
> Johan Hovold  wrote:
> 
> [...]
> > > 
> > > So to avoid having hardware information spread all over the table at least
> > > these information would need to be in devicetree. But that also all feels
> > > like a hack and hard to maintain.  
> > 
> > Having the device described in the device tree is certainly desirable,
> > not least for chip identification. And with a GPS framework in the
> > kernel with a well-defined interface, implementing power management
> > would be straight forward.
> > 
> Hmm, devicetree without in-kernel drivers, do we have anything like that
> somewhere? I thought that was a big no-go. But maybe I am wrong.

No, that's probably not a good idea, even if it may be possible (what
about ACPI then, for example?).

> > I'm just not convinced that the proposed tty interface is the right
> > interface for this. User space would still rely on gpsd for the GPS
> > protocols, and would also ultimately be managing power by killing gpsd
> > or whatever daemon that would otherwise be holding the port open.
> > 
> > Something like the generic power sequences that has been discussed
> > elsewhere might be a better fit for this if all you want to do is power
> > on and off on port open and close (and on suspend/resume). There really
> > isn't anything GPS-specific in the current proposal (besides the
> > suggested tty-device name).
> 
> So a bit like that mmc-powerseq stuff we already have?

Yeah, the generic power sequence patches were inspired by that and
intended to generalise it (e.g. to be used by the USB bus to power on
devices so that they could be enumerated). There were some issues with
that work though (which also precludes it from being used for something
like this), and it still wouldn't be sufficient to deal with the gps
device in question (which needs to monitor the incoming data).

> > But sure, that wouldn't be sufficient to deal with the
> > unknown-power-state problem with the device in question.
>
> Maybe there could be a kind of active flag set by the tty if
> there is traffic, so that active flag could be used in these
> power sequence stuff? But then again the tty layer has to be extended
> which would probably also cause a lot of ruffled feathers.

Yeah, I think this is a dead end. We need some kind of gps framework
with drivers that can implement the device specific bits.

I may have some time to look at little closer at it this week.

Johan

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Tue, Feb 27, 2018 at 08:32:50AM +0100, H. Nikolaus Schaller wrote:
> Hi Johan,
> 
> > Am 27.02.2018 um 08:04 schrieb Johan Hovold :
> > 
> > On Mon, Feb 12, 2018 at 04:26:18PM +0100, Pavel Machek wrote:
> >> Hi!
> >> 
>  Let's restart this discussion and focus on the main roadblock (others
>  are minor details which can be sorted out later).
>  
>  If it feels like a hack, the key issue seems to me to be the choice of
>  the API to present the GPS data to user space. Right?
> >>> 
> >>> Or even more fundamentally, does this belong in the kernel at all?
> >> 
> >> Yes, it does.
> 
> Thanks, Pavel for supporting our view.
> 
> > 
> > But not necessarily in its current form.
> 
> Is this a "yes after some code fixes"?

No, we need some kind of at least rudimentary gps framework even if we
allow for a raw (NMEA) interface for the time being (possibly
indefinitely).

> Pavel mentioned an example where such an evolutionary approach was taken.
> > 
> >>> Now, if we'd ever have a proper GPS framework that handled everything in
> >>> kernel space (i.e. no more gpsd) then we would be able to write kernel
> >>> drivers that also take care of PM. But perhaps that's unlikely to ever
> >>> be realised given the state of things (proprietary protocols, numerous
> >>> quirky implementations, etc).
> >> 
> >> That is what needs to happen.
> >> 
> >>> The kernel is probably not the place to be working around issues like
> >>> that, even if serdev at least allows for such hacks to be fairly
> >>> isolated in drivers (unlike some of the earlier proposals touching core
> >>> code).
> >> 
> >> Oh, kernel is indeed right place to provide hardware abstraction --
> >> and that includes bug workarounds.
> > 
> > Right, at least when such hacks can be confined to a driver and not be
> > spread all over the place.
> 
> It seems that you forgot that the driver we propose is not spread all over
> the place. It *is* confined to a single driver thanks to the serdev api.

I believe that's what I wrote above.

Johan

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Tue, Feb 27, 2018 at 08:32:50AM +0100, H. Nikolaus Schaller wrote:
> Hi Johan,
> 
> > Am 27.02.2018 um 08:04 schrieb Johan Hovold :
> > 
> > On Mon, Feb 12, 2018 at 04:26:18PM +0100, Pavel Machek wrote:
> >> Hi!
> >> 
>  Let's restart this discussion and focus on the main roadblock (others
>  are minor details which can be sorted out later).
>  
>  If it feels like a hack, the key issue seems to me to be the choice of
>  the API to present the GPS data to user space. Right?
> >>> 
> >>> Or even more fundamentally, does this belong in the kernel at all?
> >> 
> >> Yes, it does.
> 
> Thanks, Pavel for supporting our view.
> 
> > 
> > But not necessarily in its current form.
> 
> Is this a "yes after some code fixes"?

No, we need some kind of at least rudimentary gps framework even if we
allow for a raw (NMEA) interface for the time being (possibly
indefinitely).

> Pavel mentioned an example where such an evolutionary approach was taken.
> > 
> >>> Now, if we'd ever have a proper GPS framework that handled everything in
> >>> kernel space (i.e. no more gpsd) then we would be able to write kernel
> >>> drivers that also take care of PM. But perhaps that's unlikely to ever
> >>> be realised given the state of things (proprietary protocols, numerous
> >>> quirky implementations, etc).
> >> 
> >> That is what needs to happen.
> >> 
> >>> The kernel is probably not the place to be working around issues like
> >>> that, even if serdev at least allows for such hacks to be fairly
> >>> isolated in drivers (unlike some of the earlier proposals touching core
> >>> code).
> >> 
> >> Oh, kernel is indeed right place to provide hardware abstraction --
> >> and that includes bug workarounds.
> > 
> > Right, at least when such hacks can be confined to a driver and not be
> > spread all over the place.
> 
> It seems that you forgot that the driver we propose is not spread all over
> the place. It *is* confined to a single driver thanks to the serdev api.

I believe that's what I wrote above.

Johan

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Andreas Kemnade]

Hi,

On Thu, 18 Jan 2018 17:47:36 +1100
Johan Hovold  wrote:

[...]
> > 
> > So to avoid having hardware information spread all over the table at least
> > these information would need to be in devicetree. But that also all feels
> > like a hack and hard to maintain.  
> 
> Having the device described in the device tree is certainly desirable,
> not least for chip identification. And with a GPS framework in the
> kernel with a well-defined interface, implementing power management
> would be straight forward.
> 
Hmm, devicetree without in-kernel drivers, do we have anything like that
somewhere? I thought that was a big no-go. But maybe I am wrong.

> I'm just not convinced that the proposed tty interface is the right
> interface for this. User space would still rely on gpsd for the GPS
> protocols, and would also ultimately be managing power by killing gpsd
> or whatever daemon that would otherwise be holding the port open.
> 
> Something like the generic power sequences that has been discussed
> elsewhere might be a better fit for this if all you want to do is power
> on and off on port open and close (and on suspend/resume). There really
> isn't anything GPS-specific in the current proposal (besides the
> suggested tty-device name).

So a bit like that mmc-powerseq stuff we already have?
> 
> But sure, that wouldn't be sufficient to deal with the
> unknown-power-state problem with the device in question.
> 
Maybe there could be a kind of active flag set by the tty if
there is traffic, so that active flag could be used in these
power sequence stuff? But then again the tty layer has to be extended
which would probably also cause a lot of ruffled feathers.

Regards,
Andreas


pgpq27ubjUuCY.pgp
Description: OpenPGP digital signature

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Andreas Kemnade]

Hi,

On Thu, 18 Jan 2018 17:47:36 +1100
Johan Hovold  wrote:

[...]
> > 
> > So to avoid having hardware information spread all over the table at least
> > these information would need to be in devicetree. But that also all feels
> > like a hack and hard to maintain.  
> 
> Having the device described in the device tree is certainly desirable,
> not least for chip identification. And with a GPS framework in the
> kernel with a well-defined interface, implementing power management
> would be straight forward.
> 
Hmm, devicetree without in-kernel drivers, do we have anything like that
somewhere? I thought that was a big no-go. But maybe I am wrong.

> I'm just not convinced that the proposed tty interface is the right
> interface for this. User space would still rely on gpsd for the GPS
> protocols, and would also ultimately be managing power by killing gpsd
> or whatever daemon that would otherwise be holding the port open.
> 
> Something like the generic power sequences that has been discussed
> elsewhere might be a better fit for this if all you want to do is power
> on and off on port open and close (and on suspend/resume). There really
> isn't anything GPS-specific in the current proposal (besides the
> suggested tty-device name).

So a bit like that mmc-powerseq stuff we already have?
> 
> But sure, that wouldn't be sufficient to deal with the
> unknown-power-state problem with the device in question.
> 
Maybe there could be a kind of active flag set by the tty if
there is traffic, so that active flag could be used in these
power sequence stuff? But then again the tty layer has to be extended
which would probably also cause a lot of ruffled feathers.

Regards,
Andreas


pgpq27ubjUuCY.pgp
Description: OpenPGP digital signature

Re: [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Hi Johan,
I know you have a lot of other things to do, but we are still waiting for a
statement that this driver will be accepted after fixing the final coding 
issues.

Please advise on how you want to proceed with this.

One more technical comment/question/aspect below:

> Am 18.01.2018 um 14:43 schrieb H. Nikolaus Schaller :
> 
> Hi Johan,
> 
>> Am 18.01.2018 um 07:13 schrieb Johan Hovold :
>> 
>> Hacks are never good, but sometimes needed. But we should try to keep
>> them contained in drivers rather than allow them to spread to core code,
>> was what I was trying to say above.
> 
> Well, aren't we talking here about a well isolated driver? And not about
> core code?
> 
> Core code already provides everything to build a driver for this chip
> to make us happy with.
> 
> It is just not yet providing a generic gps interface API to make everybody
> happy with.
> 
>>> That is what Andreas did remark as motivation: provide a solution
>>> for *existing* user spaces.
>> 
>> I understand that this is what you want, but that in itself is not a
>> sufficient reason to put something in the kernel.
> 
> Agreed, but it is a secondary (but still strong) motivation, not the primary 
> one.
> 
>> 
> - can not guarantee (!) to power off the chip if the last user-space
> process using it is killed (which is essential for power-management of
> a handheld, battery operated device)
 
 That depends on how you implement things (extending gpsd, wrapper
 script, pty daemon, ...).
>>> 
>>> No. You can of course cover all standard cases but there is one fundamental
>>> issue which is IMHO a problem of any user-space implementation:
>>> 
>>> How can you guarantee that the chip is powered off if no
>>> user-space process is using it or if the last process doing
>>> this is killed by *whatever* reason?
>>> 
>>> E.g. after a kill -9. Or if someone deinstalls gpsd or whatever and assumes
>>> (and wants a guarantee) that GPS is now turned off and never turned on 
>>> drawing
>>> precious milliamps from the battery for no use.
>> 
>> Have something run at init to put the device in a low power state.

If I look for example at the camera module drivers provided by
drivers/media/i2c, most of them could be easily power-controlled from
user-space by i2c-tools and 1-2 gpios through /sys/class/gpio and
a big set of scripts.

Still they have a place in the kernel and cameras are powered on
if the device is opened and powered down if it is closed.

So I am still trying to understand the rationale and logic (if one exists)
behind having them in kernel but rejecting our driver which does the
same for a different class of devices.

> This does *not* solve the issue how to *guarantee* that it becomes
> powered off if the number of user-space processes goes down to zero
> *after* init.
> 
> Please consider that a portable device is rarely booted but might be
> operated over several days with many suspend cycles. And people may
> still expect that the power consumer "GPS" is turned off if their
> personal user-space setup simply kills gpsd.

> 
>> 
>>> As it is well known, a user-space process can't protect itself against kill 
>>> -9.
>>> Or has this recently been changed and I am not aware of?
>>> 
>>> This is the fundamental reason why we need a kernel driver to provide
>>> reliable, repeatable and trustable power management of this chip.
>>> 
>>> It is equally fundamental as a hard disk should spin down after the last
>>> file is closed. Even if this process ends by a kill -9.
> 
> Please advise how we should solve this fundamental problem in user-space.
> 
>>> 
>>> This seems to contradict your argument that user-space can very easily
>>> adapt to everything. If the latter were true there would be no need to
>>> keep old interfaces supported for a long time.
>> 
>> You probably know that we try hard never to change an interface that
>> would break user space, and that's why we need to get it right.
> 
> Yes, I know and agree that it is very important (and difficult to achieve).
> 
> But it seems that there are different opinions of what "right" is...
> 
> You seem to focus on the "right" API only (where we agree that the "right"
> API does not exist and likely will never come or at least in the near future).
> 
> But for us the whole combination of kernel + user-space must behave "right"
> (and use a function split that allows to optimally achieve this goal).
> 
>> 
>>> So can you agree to that a battery powered portable device must have
>>> reliable and trustable power management? And if it provable can't be
>>> implemented in user-space (a single counter example suffices) it must
>>> be a kernel driver?
>> 
>> Having a kernel driver would make things easier for user space, sure,
>> but again, that's not a sufficient reason to merge just any kernel
>> implementation.
> 
> It is not about "easier" for anyone. Neither for you nor for me. For us
> it would be much easier 

Re: [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Hi Johan,
I know you have a lot of other things to do, but we are still waiting for a
statement that this driver will be accepted after fixing the final coding 
issues.

Please advise on how you want to proceed with this.

One more technical comment/question/aspect below:

> Am 18.01.2018 um 14:43 schrieb H. Nikolaus Schaller :
> 
> Hi Johan,
> 
>> Am 18.01.2018 um 07:13 schrieb Johan Hovold :
>> 
>> Hacks are never good, but sometimes needed. But we should try to keep
>> them contained in drivers rather than allow them to spread to core code,
>> was what I was trying to say above.
> 
> Well, aren't we talking here about a well isolated driver? And not about
> core code?
> 
> Core code already provides everything to build a driver for this chip
> to make us happy with.
> 
> It is just not yet providing a generic gps interface API to make everybody
> happy with.
> 
>>> That is what Andreas did remark as motivation: provide a solution
>>> for *existing* user spaces.
>> 
>> I understand that this is what you want, but that in itself is not a
>> sufficient reason to put something in the kernel.
> 
> Agreed, but it is a secondary (but still strong) motivation, not the primary 
> one.
> 
>> 
> - can not guarantee (!) to power off the chip if the last user-space
> process using it is killed (which is essential for power-management of
> a handheld, battery operated device)
 
 That depends on how you implement things (extending gpsd, wrapper
 script, pty daemon, ...).
>>> 
>>> No. You can of course cover all standard cases but there is one fundamental
>>> issue which is IMHO a problem of any user-space implementation:
>>> 
>>> How can you guarantee that the chip is powered off if no
>>> user-space process is using it or if the last process doing
>>> this is killed by *whatever* reason?
>>> 
>>> E.g. after a kill -9. Or if someone deinstalls gpsd or whatever and assumes
>>> (and wants a guarantee) that GPS is now turned off and never turned on 
>>> drawing
>>> precious milliamps from the battery for no use.
>> 
>> Have something run at init to put the device in a low power state.

If I look for example at the camera module drivers provided by
drivers/media/i2c, most of them could be easily power-controlled from
user-space by i2c-tools and 1-2 gpios through /sys/class/gpio and
a big set of scripts.

Still they have a place in the kernel and cameras are powered on
if the device is opened and powered down if it is closed.

So I am still trying to understand the rationale and logic (if one exists)
behind having them in kernel but rejecting our driver which does the
same for a different class of devices.

> This does *not* solve the issue how to *guarantee* that it becomes
> powered off if the number of user-space processes goes down to zero
> *after* init.
> 
> Please consider that a portable device is rarely booted but might be
> operated over several days with many suspend cycles. And people may
> still expect that the power consumer "GPS" is turned off if their
> personal user-space setup simply kills gpsd.

> 
>> 
>>> As it is well known, a user-space process can't protect itself against kill 
>>> -9.
>>> Or has this recently been changed and I am not aware of?
>>> 
>>> This is the fundamental reason why we need a kernel driver to provide
>>> reliable, repeatable and trustable power management of this chip.
>>> 
>>> It is equally fundamental as a hard disk should spin down after the last
>>> file is closed. Even if this process ends by a kill -9.
> 
> Please advise how we should solve this fundamental problem in user-space.
> 
>>> 
>>> This seems to contradict your argument that user-space can very easily
>>> adapt to everything. If the latter were true there would be no need to
>>> keep old interfaces supported for a long time.
>> 
>> You probably know that we try hard never to change an interface that
>> would break user space, and that's why we need to get it right.
> 
> Yes, I know and agree that it is very important (and difficult to achieve).
> 
> But it seems that there are different opinions of what "right" is...
> 
> You seem to focus on the "right" API only (where we agree that the "right"
> API does not exist and likely will never come or at least in the near future).
> 
> But for us the whole combination of kernel + user-space must behave "right"
> (and use a function split that allows to optimally achieve this goal).
> 
>> 
>>> So can you agree to that a battery powered portable device must have
>>> reliable and trustable power management? And if it provable can't be
>>> implemented in user-space (a single counter example suffices) it must
>>> be a kernel driver?
>> 
>> Having a kernel driver would make things easier for user space, sure,
>> but again, that's not a sufficient reason to merge just any kernel
>> implementation.
> 
> It is not about "easier" for anyone. Neither for you nor for me. For us
> it would be much easier not to have to run this never-ending 

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Pavel Machek]

Hi!

> > > > Let's restart this discussion and focus on the main roadblock (others
> > > > are minor details which can be sorted out later).
> > > > 
> > > > If it feels like a hack, the key issue seems to me to be the choice of
> > > > the API to present the GPS data to user space. Right?
> > > 
> > > Or even more fundamentally, does this belong in the kernel at all?
> > 
> > Yes, it does.
> 
> But not necessarily in its current form.

Not necessarily, no. OTOH this hack was not too bad IIRC and we
usually do present NMEA to userspace at the moment. We'll need proper
GPS subsystem one day, but I'm afraid that will take some time...

Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) 
http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Pavel Machek]

Hi!

> > > > Let's restart this discussion and focus on the main roadblock (others
> > > > are minor details which can be sorted out later).
> > > > 
> > > > If it feels like a hack, the key issue seems to me to be the choice of
> > > > the API to present the GPS data to user space. Right?
> > > 
> > > Or even more fundamentally, does this belong in the kernel at all?
> > 
> > Yes, it does.
> 
> But not necessarily in its current form.

Not necessarily, no. OTOH this hack was not too bad IIRC and we
usually do present NMEA to userspace at the moment. We'll need proper
GPS subsystem one day, but I'm afraid that will take some time...

Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) 
http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Hi Johan,

> Am 27.02.2018 um 08:04 schrieb Johan Hovold :
> 
> On Mon, Feb 12, 2018 at 04:26:18PM +0100, Pavel Machek wrote:
>> Hi!
>> 
 Let's restart this discussion and focus on the main roadblock (others
 are minor details which can be sorted out later).
 
 If it feels like a hack, the key issue seems to me to be the choice of
 the API to present the GPS data to user space. Right?
>>> 
>>> Or even more fundamentally, does this belong in the kernel at all?
>> 
>> Yes, it does.

Thanks, Pavel for supporting our view.

> 
> But not necessarily in its current form.

Is this a "yes after some code fixes"?

Pavel mentioned an example where such an evolutionary approach was taken.

> 
>>> Now, if we'd ever have a proper GPS framework that handled everything in
>>> kernel space (i.e. no more gpsd) then we would be able to write kernel
>>> drivers that also take care of PM. But perhaps that's unlikely to ever
>>> be realised given the state of things (proprietary protocols, numerous
>>> quirky implementations, etc).
>> 
>> That is what needs to happen.
>> 
>>> The kernel is probably not the place to be working around issues like
>>> that, even if serdev at least allows for such hacks to be fairly
>>> isolated in drivers (unlike some of the earlier proposals touching core
>>> code).
>> 
>> Oh, kernel is indeed right place to provide hardware abstraction --
>> and that includes bug workarounds.
> 
> Right, at least when such hacks can be confined to a driver and not be
> spread all over the place.

It seems that you forgot that the driver we propose is not spread all over
the place. It *is* confined to a single driver thanks to the serdev api.

BR and thanks,
Nikolaus

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Hi Johan,

> Am 27.02.2018 um 08:04 schrieb Johan Hovold :
> 
> On Mon, Feb 12, 2018 at 04:26:18PM +0100, Pavel Machek wrote:
>> Hi!
>> 
 Let's restart this discussion and focus on the main roadblock (others
 are minor details which can be sorted out later).
 
 If it feels like a hack, the key issue seems to me to be the choice of
 the API to present the GPS data to user space. Right?
>>> 
>>> Or even more fundamentally, does this belong in the kernel at all?
>> 
>> Yes, it does.

Thanks, Pavel for supporting our view.

> 
> But not necessarily in its current form.

Is this a "yes after some code fixes"?

Pavel mentioned an example where such an evolutionary approach was taken.

> 
>>> Now, if we'd ever have a proper GPS framework that handled everything in
>>> kernel space (i.e. no more gpsd) then we would be able to write kernel
>>> drivers that also take care of PM. But perhaps that's unlikely to ever
>>> be realised given the state of things (proprietary protocols, numerous
>>> quirky implementations, etc).
>> 
>> That is what needs to happen.
>> 
>>> The kernel is probably not the place to be working around issues like
>>> that, even if serdev at least allows for such hacks to be fairly
>>> isolated in drivers (unlike some of the earlier proposals touching core
>>> code).
>> 
>> Oh, kernel is indeed right place to provide hardware abstraction --
>> and that includes bug workarounds.
> 
> Right, at least when such hacks can be confined to a driver and not be
> spread all over the place.

It seems that you forgot that the driver we propose is not spread all over
the place. It *is* confined to a single driver thanks to the serdev api.

BR and thanks,
Nikolaus

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Mon, Feb 12, 2018 at 04:26:18PM +0100, Pavel Machek wrote:
> Hi!
> 
> > > Let's restart this discussion and focus on the main roadblock (others
> > > are minor details which can be sorted out later).
> > > 
> > > If it feels like a hack, the key issue seems to me to be the choice of
> > > the API to present the GPS data to user space. Right?
> > 
> > Or even more fundamentally, does this belong in the kernel at all?
> 
> Yes, it does.

But not necessarily in its current form.

> > Now, if we'd ever have a proper GPS framework that handled everything in
> > kernel space (i.e. no more gpsd) then we would be able to write kernel
> > drivers that also take care of PM. But perhaps that's unlikely to ever
> > be realised given the state of things (proprietary protocols, numerous
> > quirky implementations, etc).
> 
> That is what needs to happen.
> 
> > The kernel is probably not the place to be working around issues like
> > that, even if serdev at least allows for such hacks to be fairly
> > isolated in drivers (unlike some of the earlier proposals touching core
> > code).
> 
> Oh, kernel is indeed right place to provide hardware abstraction --
> and that includes bug workarounds.

Right, at least when such hacks can be confined to a driver and not be
spread all over the place.

Johan

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Mon, Feb 12, 2018 at 04:26:18PM +0100, Pavel Machek wrote:
> Hi!
> 
> > > Let's restart this discussion and focus on the main roadblock (others
> > > are minor details which can be sorted out later).
> > > 
> > > If it feels like a hack, the key issue seems to me to be the choice of
> > > the API to present the GPS data to user space. Right?
> > 
> > Or even more fundamentally, does this belong in the kernel at all?
> 
> Yes, it does.

But not necessarily in its current form.

> > Now, if we'd ever have a proper GPS framework that handled everything in
> > kernel space (i.e. no more gpsd) then we would be able to write kernel
> > drivers that also take care of PM. But perhaps that's unlikely to ever
> > be realised given the state of things (proprietary protocols, numerous
> > quirky implementations, etc).
> 
> That is what needs to happen.
> 
> > The kernel is probably not the place to be working around issues like
> > that, even if serdev at least allows for such hacks to be fairly
> > isolated in drivers (unlike some of the earlier proposals touching core
> > code).
> 
> Oh, kernel is indeed right place to provide hardware abstraction --
> and that includes bug workarounds.

Right, at least when such hacks can be confined to a driver and not be
spread all over the place.

Johan

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Pavel Machek]

Hi!

> > Let's restart this discussion and focus on the main roadblock (others
> > are minor details which can be sorted out later).
> > 
> > If it feels like a hack, the key issue seems to me to be the choice of
> > the API to present the GPS data to user space. Right?
> 
> Or even more fundamentally, does this belong in the kernel at all?

Yes, it does.

> Given that we'd still depend on gpsd and other, proprietary, daemons to
> actually parse and use (also for control) the plethora of GPS protocols
> available, it may even be best to just keep it all in user space.

No. We'd want to move away from gpsd in the long
term. (/dev/input/mice was in similar situation.)

> Now, if we'd ever have a proper GPS framework that handled everything in
> kernel space (i.e. no more gpsd) then we would be able to write kernel
> drivers that also take care of PM. But perhaps that's unlikely to ever
> be realised given the state of things (proprietary protocols, numerous
> quirky implementations, etc).

That is what needs to happen.

> The kernel is probably not the place to be working around issues like
> that, even if serdev at least allows for such hacks to be fairly
> isolated in drivers (unlike some of the earlier proposals touching core
> code).

Oh, kernel is indeed right place to provide hardware abstraction --
and that includes bug workarounds.

We'd like unmodified userspace to run on any supported hardware,
remember?

Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) 
http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Pavel Machek]

Hi!

> >> I'm sorry (and I know this discussion has been going on for a long
> >> time),but this still feels like too much of a hack.
> 
> Happy new year ... Happy new attempt...
> 
> Let's restart this discussion and focus on the main roadblock (others are 
> minor
> details which can be sorted out later).
> 
> If it feels like a hack, the key issue seems to me to be the choice of
> the API to present the GPS data to user space. Right?
> 
> I see three reasonable options how this presentation can be done:
> 
> 1. char device
> 2. tty device
> 3. some new gps interface API (similar to network, bluetooth interfaces)
> 4. no driver and use the UART tty directly

> 3. some new gps interface API
> + could become very elegant and general
> - does not exist (AFAIK not even a plan but I am not aware of everything)
> - no user-space daemons and applications exist which use it

Yes, that is what needs to be done. It is very similar problem to
serial mice we used to have long time ago. (And it has pretty much
same solution; exporting NMEA for gpsd, then slowly moving to system
with no gpsd).

Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) 
http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Pavel Machek]

Hi!

> > Let's restart this discussion and focus on the main roadblock (others
> > are minor details which can be sorted out later).
> > 
> > If it feels like a hack, the key issue seems to me to be the choice of
> > the API to present the GPS data to user space. Right?
> 
> Or even more fundamentally, does this belong in the kernel at all?

Yes, it does.

> Given that we'd still depend on gpsd and other, proprietary, daemons to
> actually parse and use (also for control) the plethora of GPS protocols
> available, it may even be best to just keep it all in user space.

No. We'd want to move away from gpsd in the long
term. (/dev/input/mice was in similar situation.)

> Now, if we'd ever have a proper GPS framework that handled everything in
> kernel space (i.e. no more gpsd) then we would be able to write kernel
> drivers that also take care of PM. But perhaps that's unlikely to ever
> be realised given the state of things (proprietary protocols, numerous
> quirky implementations, etc).

That is what needs to happen.

> The kernel is probably not the place to be working around issues like
> that, even if serdev at least allows for such hacks to be fairly
> isolated in drivers (unlike some of the earlier proposals touching core
> code).

Oh, kernel is indeed right place to provide hardware abstraction --
and that includes bug workarounds.

We'd like unmodified userspace to run on any supported hardware,
remember?

Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) 
http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


signature.asc
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Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Pavel Machek]

Hi!

> >> I'm sorry (and I know this discussion has been going on for a long
> >> time),but this still feels like too much of a hack.
> 
> Happy new year ... Happy new attempt...
> 
> Let's restart this discussion and focus on the main roadblock (others are 
> minor
> details which can be sorted out later).
> 
> If it feels like a hack, the key issue seems to me to be the choice of
> the API to present the GPS data to user space. Right?
> 
> I see three reasonable options how this presentation can be done:
> 
> 1. char device
> 2. tty device
> 3. some new gps interface API (similar to network, bluetooth interfaces)
> 4. no driver and use the UART tty directly

> 3. some new gps interface API
> + could become very elegant and general
> - does not exist (AFAIK not even a plan but I am not aware of everything)
> - no user-space daemons and applications exist which use it

Yes, that is what needs to be done. It is very similar problem to
serial mice we used to have long time ago. (And it has pretty much
same solution; exporting NMEA for gpsd, then slowly moving to system
with no gpsd).

Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) 
http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


signature.asc
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Re: [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Hi Johan,

> Am 18.01.2018 um 07:13 schrieb Johan Hovold :
> 
> Hacks are never good, but sometimes needed. But we should try to keep
> them contained in drivers rather than allow them to spread to core code,
> was what I was trying to say above.

Well, aren't we talking here about a well isolated driver? And not about
core code?

Core code already provides everything to build a driver for this chip
to make us happy with.

It is just not yet providing a generic gps interface API to make everybody
happy with.

>> That is what Andreas did remark as motivation: provide a solution
>> for *existing* user spaces.
> 
> I understand that this is what you want, but that in itself is not a
> sufficient reason to put something in the kernel.

Agreed, but it is a secondary (but still strong) motivation, not the primary 
one.

> 
 - can not guarantee (!) to power off the chip if the last user-space
 process using it is killed (which is essential for power-management of
 a handheld, battery operated device)
>>> 
>>> That depends on how you implement things (extending gpsd, wrapper
>>> script, pty daemon, ...).
>> 
>> No. You can of course cover all standard cases but there is one fundamental
>> issue which is IMHO a problem of any user-space implementation:
>> 
>>  How can you guarantee that the chip is powered off if no
>>  user-space process is using it or if the last process doing
>>  this is killed by *whatever* reason?
>> 
>> E.g. after a kill -9. Or if someone deinstalls gpsd or whatever and assumes
>> (and wants a guarantee) that GPS is now turned off and never turned on 
>> drawing
>> precious milliamps from the battery for no use.
> 
> Have something run at init to put the device in a low power state.

This does *not* solve the issue how to *guarantee* that it becomes
powered off if the number of user-space processes goes down to zero
*after* init.

Please consider that a portable device is rarely booted but might be
operated over several days with many suspend cycles. And people may
still expect that the power consumer "GPS" is turned off if their
personal user-space setup simply kills gpsd.

> 
>> As it is well known, a user-space process can't protect itself against kill 
>> -9.
>> Or has this recently been changed and I am not aware of?
>> 
>> This is the fundamental reason why we need a kernel driver to provide
>> reliable, repeatable and trustable power management of this chip.
>> 
>> It is equally fundamental as a hard disk should spin down after the last
>> file is closed. Even if this process ends by a kill -9.

Please advise how we should solve this fundamental problem in user-space.

>> 
>> This seems to contradict your argument that user-space can very easily
>> adapt to everything. If the latter were true there would be no need to
>> keep old interfaces supported for a long time.
> 
> You probably know that we try hard never to change an interface that
> would break user space, and that's why we need to get it right.

Yes, I know and agree that it is very important (and difficult to achieve).

But it seems that there are different opinions of what "right" is...

You seem to focus on the "right" API only (where we agree that the "right"
API does not exist and likely will never come or at least in the near future).

But for us the whole combination of kernel + user-space must behave "right"
(and use a function split that allows to optimally achieve this goal).

> 
>> So can you agree to that a battery powered portable device must have
>> reliable and trustable power management? And if it provable can't be
>> implemented in user-space (a single counter example suffices) it must
>> be a kernel driver?
> 
> Having a kernel driver would make things easier for user space, sure,
> but again, that's not a sufficient reason to merge just any kernel
> implementation.

It is not about "easier" for anyone. Neither for you nor for me. For us
it would be much easier not to have to run this never-ending discussion
over and over...

It is about making it technically fully "reliable". And not 99% as per
quick and dirty user-space hacks.

It is so easy to invent scenarios in user-space to make the device practically
unusable by unnoticed draining a full battery within less than a day when
not perfectly turning off the chip power.

So if a kernel driver can better protect users against this situation for
a portable device with this chip, why shouldn't it do with a handful LOC?
What requirement is more important than this?

BR and thanks,
Nikolaus

Re: [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Hi Johan,

> Am 18.01.2018 um 07:13 schrieb Johan Hovold :
> 
> Hacks are never good, but sometimes needed. But we should try to keep
> them contained in drivers rather than allow them to spread to core code,
> was what I was trying to say above.

Well, aren't we talking here about a well isolated driver? And not about
core code?

Core code already provides everything to build a driver for this chip
to make us happy with.

It is just not yet providing a generic gps interface API to make everybody
happy with.

>> That is what Andreas did remark as motivation: provide a solution
>> for *existing* user spaces.
> 
> I understand that this is what you want, but that in itself is not a
> sufficient reason to put something in the kernel.

Agreed, but it is a secondary (but still strong) motivation, not the primary 
one.

> 
 - can not guarantee (!) to power off the chip if the last user-space
 process using it is killed (which is essential for power-management of
 a handheld, battery operated device)
>>> 
>>> That depends on how you implement things (extending gpsd, wrapper
>>> script, pty daemon, ...).
>> 
>> No. You can of course cover all standard cases but there is one fundamental
>> issue which is IMHO a problem of any user-space implementation:
>> 
>>  How can you guarantee that the chip is powered off if no
>>  user-space process is using it or if the last process doing
>>  this is killed by *whatever* reason?
>> 
>> E.g. after a kill -9. Or if someone deinstalls gpsd or whatever and assumes
>> (and wants a guarantee) that GPS is now turned off and never turned on 
>> drawing
>> precious milliamps from the battery for no use.
> 
> Have something run at init to put the device in a low power state.

This does *not* solve the issue how to *guarantee* that it becomes
powered off if the number of user-space processes goes down to zero
*after* init.

Please consider that a portable device is rarely booted but might be
operated over several days with many suspend cycles. And people may
still expect that the power consumer "GPS" is turned off if their
personal user-space setup simply kills gpsd.

> 
>> As it is well known, a user-space process can't protect itself against kill 
>> -9.
>> Or has this recently been changed and I am not aware of?
>> 
>> This is the fundamental reason why we need a kernel driver to provide
>> reliable, repeatable and trustable power management of this chip.
>> 
>> It is equally fundamental as a hard disk should spin down after the last
>> file is closed. Even if this process ends by a kill -9.

Please advise how we should solve this fundamental problem in user-space.

>> 
>> This seems to contradict your argument that user-space can very easily
>> adapt to everything. If the latter were true there would be no need to
>> keep old interfaces supported for a long time.
> 
> You probably know that we try hard never to change an interface that
> would break user space, and that's why we need to get it right.

Yes, I know and agree that it is very important (and difficult to achieve).

But it seems that there are different opinions of what "right" is...

You seem to focus on the "right" API only (where we agree that the "right"
API does not exist and likely will never come or at least in the near future).

But for us the whole combination of kernel + user-space must behave "right"
(and use a function split that allows to optimally achieve this goal).

> 
>> So can you agree to that a battery powered portable device must have
>> reliable and trustable power management? And if it provable can't be
>> implemented in user-space (a single counter example suffices) it must
>> be a kernel driver?
> 
> Having a kernel driver would make things easier for user space, sure,
> but again, that's not a sufficient reason to merge just any kernel
> implementation.

It is not about "easier" for anyone. Neither for you nor for me. For us
it would be much easier not to have to run this never-ending discussion
over and over...

It is about making it technically fully "reliable". And not 99% as per
quick and dirty user-space hacks.

It is so easy to invent scenarios in user-space to make the device practically
unusable by unnoticed draining a full battery within less than a day when
not perfectly turning off the chip power.

So if a kernel driver can better protect users against this situation for
a portable device with this chip, why shouldn't it do with a handful LOC?
What requirement is more important than this?

BR and thanks,
Nikolaus

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Fri, Jan 12, 2018 at 07:40:35PM +0100, Andreas Kemnade wrote:
> On Fri, 12 Jan 2018 15:46:47 +0100
> Johan Hovold  wrote:
> 
> > On Tue, Jan 09, 2018 at 06:43:47PM +0100, Andreas Kemnade wrote:
> > > On Fri, 22 Dec 2017 13:44:27 +0100
> > > Johan Hovold  wrote:
> > > 
> > > [...]  
> > > > I'd suggest reiterating the problem you're trying to solve and
> > > > enumerating the previously discussed potential solutions in order to
> > > > find a proper abstraction level for this (before getting lost in
> > > > implementation details).
> > > >   
> > > The main point here is in short words: Having a device powered on or off
> > > when the uart it is attached to, is used or not used anymore,
> > > so the already available userspace applications do not need to be 
> > > changed.  
> > 
> > So we'd end up with something in-between a kernel driver and a
> > user-space solution. What about devices that need to be (partially)
> > powered also when the port isn't open? A pure user-space solution would
> > be able to handle all variants.
> > 
> Well partly powered devices are at many places, And they hide that problem
> from userspace, just get the open()/get() and close()/put() from there and 
> power the
> device accordingly. 
> 
> So the question still remains why should the kernel hide some things and some
> it should not.
> If it all is in userspace, then there is still something needed in the 
> devicetree
> (if I understand correctly, every information about hardware which cannot be
> auto-probed belongs into device tree) so that the userspace knows what kind of
> device is at that port. So there can be a daemon powering on and off devices.
> But that would break existing applications which just expect that they just 
> need
> to open/close the device. 
> 
> Or you need to have some inotify handler in userspace and attach it there to
> react on close() and open() of that device.
> But this thing needs to have two kind of information:
> 
> 1. the type of chip available to do the right powerup sequence. 
> 
> 2. how the chip is wired up to the cpu. 
> 
> So to avoid having hardware information spread all over the table at least
> these information would need to be in devicetree. But that also all feels
> like a hack and hard to maintain.

Having the device described in the device tree is certainly desirable,
not least for chip identification. And with a GPS framework in the
kernel with a well-defined interface, implementing power management
would be straight forward.

I'm just not convinced that the proposed tty interface is the right
interface for this. User space would still rely on gpsd for the GPS
protocols, and would also ultimately be managing power by killing gpsd
or whatever daemon that would otherwise be holding the port open.

Something like the generic power sequences that has been discussed
elsewhere might be a better fit for this if all you want to do is power
on and off on port open and close (and on suspend/resume). There really
isn't anything GPS-specific in the current proposal (besides the
suggested tty-device name).

But sure, that wouldn't be sufficient to deal with the
unknown-power-state problem with the device in question.

Johan

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Fri, Jan 12, 2018 at 07:40:35PM +0100, Andreas Kemnade wrote:
> On Fri, 12 Jan 2018 15:46:47 +0100
> Johan Hovold  wrote:
> 
> > On Tue, Jan 09, 2018 at 06:43:47PM +0100, Andreas Kemnade wrote:
> > > On Fri, 22 Dec 2017 13:44:27 +0100
> > > Johan Hovold  wrote:
> > > 
> > > [...]  
> > > > I'd suggest reiterating the problem you're trying to solve and
> > > > enumerating the previously discussed potential solutions in order to
> > > > find a proper abstraction level for this (before getting lost in
> > > > implementation details).
> > > >   
> > > The main point here is in short words: Having a device powered on or off
> > > when the uart it is attached to, is used or not used anymore,
> > > so the already available userspace applications do not need to be 
> > > changed.  
> > 
> > So we'd end up with something in-between a kernel driver and a
> > user-space solution. What about devices that need to be (partially)
> > powered also when the port isn't open? A pure user-space solution would
> > be able to handle all variants.
> > 
> Well partly powered devices are at many places, And they hide that problem
> from userspace, just get the open()/get() and close()/put() from there and 
> power the
> device accordingly. 
> 
> So the question still remains why should the kernel hide some things and some
> it should not.
> If it all is in userspace, then there is still something needed in the 
> devicetree
> (if I understand correctly, every information about hardware which cannot be
> auto-probed belongs into device tree) so that the userspace knows what kind of
> device is at that port. So there can be a daemon powering on and off devices.
> But that would break existing applications which just expect that they just 
> need
> to open/close the device. 
> 
> Or you need to have some inotify handler in userspace and attach it there to
> react on close() and open() of that device.
> But this thing needs to have two kind of information:
> 
> 1. the type of chip available to do the right powerup sequence. 
> 
> 2. how the chip is wired up to the cpu. 
> 
> So to avoid having hardware information spread all over the table at least
> these information would need to be in devicetree. But that also all feels
> like a hack and hard to maintain.

Having the device described in the device tree is certainly desirable,
not least for chip identification. And with a GPS framework in the
kernel with a well-defined interface, implementing power management
would be straight forward.

I'm just not convinced that the proposed tty interface is the right
interface for this. User space would still rely on gpsd for the GPS
protocols, and would also ultimately be managing power by killing gpsd
or whatever daemon that would otherwise be holding the port open.

Something like the generic power sequences that has been discussed
elsewhere might be a better fit for this if all you want to do is power
on and off on port open and close (and on suspend/resume). There really
isn't anything GPS-specific in the current proposal (besides the
suggested tty-device name).

But sure, that wouldn't be sufficient to deal with the
unknown-power-state problem with the device in question.

Johan

Re: [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Fri, Jan 12, 2018 at 06:59:59PM +0100, H. Nikolaus Schaller wrote:
> Hi Johan,
> 
> > Am 12.01.2018 um 16:39 schrieb Johan Hovold :
> > 
> >> Let's restart this discussion and focus on the main roadblock (others
> >> are minor details which can be sorted out later).
> >> 
> >> If it feels like a hack, the key issue seems to me to be the choice of
> >> the API to present the GPS data to user space. Right?
> > 
> > Or even more fundamentally, does this belong in the kernel at all?
> 
> Yes, that can be questioned of course. It was questioned and discussed
> several times and I thought the answer was a clear yes. But let's reiterate.
> 
> > Also it seems at least part of your specific problem is that you have
> > failed to wire up the WAKEUP pin of the W2SG0004/84 properly,
> 
> The w2sg0004 has no wakeup pin. At least I can't find one in the data sheet.

I should have said w2sg0084 above, which is the only datasheet I have found.

> The two pins you refer to from the 0084 data sheet are called BootSelect0/1
> in the 0004 and have a different function.
> 
> To be clear, we did not fail to wire it up. We did the design before the
> 0084 was announced and available. We just had to swap in the 0084 into
> existing PCBs during production because the 0004 became EOL. Otherwise
> we would probably still use the 0004 without WAKEUP output.
> 
> To make it worse, we have no documentation for an individual board if
> an 0004 or 0084 chip is installed and there is no means how a software
> can find out which one it is talking to (especially before properly
> powering on). Therefore we can not even provide two different device
> trees or drivers or whatever, unless we ask people to open their device
> and look on the chip. Quite crazy wrt. user-friendlyness of software
> installation in 2018...
> 
> Therefore, a driver must be capable to handle both chips in the same way,
> with minimalistic assumptions, even if the 0084 could provide a direct
> signal to make it easier than using serdev to monitor the data stream.

Fair enough.

> >  which then
> > forces you to look at the data stream to determine the power state of
> > the chip. Judging from a quick look at the GTA04 schematics it seems
> > you've even connected the WAKEUP output to the 1V8_OUT output?!
> 
> No. You failed to see that this is an optional 0R, which is not installed.
> The 0R on pin 7 (BootSelect1) to GND was removed when we did switch from
> 0004 to 0084. Pin 6 (BootSelect0/WAKEUP) was never connected.

Ok.

> > The kernel is probably not the place to be working around issues like
> > that,

> > even if serdev at least allows for such hacks to be fairly
> > isolated in drivers (unlike some of the earlier proposals touching core
> > code).
> 
> Please tell me why there are so many hacks for hardware issues in certain
> drivers. Any why those are good and this one (if it is one at all) is not.

Hacks are never good, but sometimes needed. But we should try to keep
them contained in drivers rather than allow them to spread to core code,
was what I was trying to say above.

> What I can learn from your discussion is that it might be considerable
> to add an optional gpio for the 0084 WAKEUP and add some logic to
> support users who have or will have that pin connected.
> 
> But even then we would need a driver to handle this gpio and issue
> an on/off impulse on the other to switch states. It would be a different
> driver (variant - maybe some CONFIG option or handled by code), but not
> "no driver".

Having a WAKEUP signal would allow for a more straight-forward
implementation, be it in the kernel or in user space.

> >> I see three reasonable options how this presentation can be done:
> >> 
> >> 1. char device
> >> 2. tty device
> >> 3. some new gps interface API (similar to network, bluetooth interfaces)
> >> 4. no driver and use the UART tty directly
> >> 
> >> Pros and cons:
> > 
> >> 4. no driver and use UART directly
> >> + a non-solution seems to be attractive
> >> - must turn on/off chip by gpio hacks from user-space
> > 
> > I'm not sure that would amount to more of hack then doing it in the
> > kernel would.
> 
> It might not be big effort in the user-space code/scripts.
> 
> But much effort to convince all the plethora of user-space client maintainers
> to integrate something. And have them roll out. And have distributions take 
> it.
> And have users upgrade to it. 5 years later...
> 
> Do you think it is easier to convince them than you? They usually assume a
> power management issue should be solved by the kernel driver.
> 
> That is what Andreas did remark as motivation: provide a solution
> for *existing* user spaces.

I understand that this is what you want, but that in itself is not a
sufficient reason to put something in the kernel.

> >> - can not guarantee (!) to power off the chip if the last user-space
> >> process using it is killed (which is essential for power-management of
> >> a handheld, battery operated 

Re: [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Fri, Jan 12, 2018 at 06:59:59PM +0100, H. Nikolaus Schaller wrote:
> Hi Johan,
> 
> > Am 12.01.2018 um 16:39 schrieb Johan Hovold :
> > 
> >> Let's restart this discussion and focus on the main roadblock (others
> >> are minor details which can be sorted out later).
> >> 
> >> If it feels like a hack, the key issue seems to me to be the choice of
> >> the API to present the GPS data to user space. Right?
> > 
> > Or even more fundamentally, does this belong in the kernel at all?
> 
> Yes, that can be questioned of course. It was questioned and discussed
> several times and I thought the answer was a clear yes. But let's reiterate.
> 
> > Also it seems at least part of your specific problem is that you have
> > failed to wire up the WAKEUP pin of the W2SG0004/84 properly,
> 
> The w2sg0004 has no wakeup pin. At least I can't find one in the data sheet.

I should have said w2sg0084 above, which is the only datasheet I have found.

> The two pins you refer to from the 0084 data sheet are called BootSelect0/1
> in the 0004 and have a different function.
> 
> To be clear, we did not fail to wire it up. We did the design before the
> 0084 was announced and available. We just had to swap in the 0084 into
> existing PCBs during production because the 0004 became EOL. Otherwise
> we would probably still use the 0004 without WAKEUP output.
> 
> To make it worse, we have no documentation for an individual board if
> an 0004 or 0084 chip is installed and there is no means how a software
> can find out which one it is talking to (especially before properly
> powering on). Therefore we can not even provide two different device
> trees or drivers or whatever, unless we ask people to open their device
> and look on the chip. Quite crazy wrt. user-friendlyness of software
> installation in 2018...
> 
> Therefore, a driver must be capable to handle both chips in the same way,
> with minimalistic assumptions, even if the 0084 could provide a direct
> signal to make it easier than using serdev to monitor the data stream.

Fair enough.

> >  which then
> > forces you to look at the data stream to determine the power state of
> > the chip. Judging from a quick look at the GTA04 schematics it seems
> > you've even connected the WAKEUP output to the 1V8_OUT output?!
> 
> No. You failed to see that this is an optional 0R, which is not installed.
> The 0R on pin 7 (BootSelect1) to GND was removed when we did switch from
> 0004 to 0084. Pin 6 (BootSelect0/WAKEUP) was never connected.

Ok.

> > The kernel is probably not the place to be working around issues like
> > that,

> > even if serdev at least allows for such hacks to be fairly
> > isolated in drivers (unlike some of the earlier proposals touching core
> > code).
> 
> Please tell me why there are so many hacks for hardware issues in certain
> drivers. Any why those are good and this one (if it is one at all) is not.

Hacks are never good, but sometimes needed. But we should try to keep
them contained in drivers rather than allow them to spread to core code,
was what I was trying to say above.

> What I can learn from your discussion is that it might be considerable
> to add an optional gpio for the 0084 WAKEUP and add some logic to
> support users who have or will have that pin connected.
> 
> But even then we would need a driver to handle this gpio and issue
> an on/off impulse on the other to switch states. It would be a different
> driver (variant - maybe some CONFIG option or handled by code), but not
> "no driver".

Having a WAKEUP signal would allow for a more straight-forward
implementation, be it in the kernel or in user space.

> >> I see three reasonable options how this presentation can be done:
> >> 
> >> 1. char device
> >> 2. tty device
> >> 3. some new gps interface API (similar to network, bluetooth interfaces)
> >> 4. no driver and use the UART tty directly
> >> 
> >> Pros and cons:
> > 
> >> 4. no driver and use UART directly
> >> + a non-solution seems to be attractive
> >> - must turn on/off chip by gpio hacks from user-space
> > 
> > I'm not sure that would amount to more of hack then doing it in the
> > kernel would.
> 
> It might not be big effort in the user-space code/scripts.
> 
> But much effort to convince all the plethora of user-space client maintainers
> to integrate something. And have them roll out. And have distributions take 
> it.
> And have users upgrade to it. 5 years later...
> 
> Do you think it is easier to convince them than you? They usually assume a
> power management issue should be solved by the kernel driver.
> 
> That is what Andreas did remark as motivation: provide a solution
> for *existing* user spaces.

I understand that this is what you want, but that in itself is not a
sufficient reason to put something in the kernel.

> >> - can not guarantee (!) to power off the chip if the last user-space
> >> process using it is killed (which is essential for power-management of
> >> a handheld, battery operated device)
> > 
> > 

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Andreas Kemnade]

On Fri, 12 Jan 2018 15:46:47 +0100
Johan Hovold  wrote:

> On Tue, Jan 09, 2018 at 06:43:47PM +0100, Andreas Kemnade wrote:
> > On Fri, 22 Dec 2017 13:44:27 +0100
> > Johan Hovold  wrote:
> > 
> > [...]  
> > > I'd suggest reiterating the problem you're trying to solve and
> > > enumerating the previously discussed potential solutions in order to
> > > find a proper abstraction level for this (before getting lost in
> > > implementation details).
> > >   
> > The main point here is in short words: Having a device powered on or off
> > when the uart it is attached to, is used or not used anymore,
> > so the already available userspace applications do not need to be changed.  
> 
> So we'd end up with something in-between a kernel driver and a
> user-space solution. What about devices that need to be (partially)
> powered also when the port isn't open? A pure user-space solution would
> be able to handle all variants.
> 
Well partly powered devices are at many places, And they hide that problem
from userspace, just get the open()/get() and close()/put() from there and 
power the
device accordingly. 

So the question still remains why should the kernel hide some things and some
it should not.
If it all is in userspace, then there is still something needed in the 
devicetree
(if I understand correctly, every information about hardware which cannot be
auto-probed belongs into device tree) so that the userspace knows what kind of
device is at that port. So there can be a daemon powering on and off devices.
But that would break existing applications which just expect that they just need
to open/close the device. 

Or you need to have some inotify handler in userspace and attach it there to
react on close() and open() of that device.
But this thing needs to have two kind of information:

1. the type of chip available to do the right powerup sequence. 

2. how the chip is wired up to the cpu. 

So to avoid having hardware information spread all over the table at least
these information would need to be in devicetree. But that also all feels
like a hack and hard to maintain.

Regards,
Andreas


pgpUTBsCJ8UuT.pgp
Description: OpenPGP digital signature

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Andreas Kemnade]

On Fri, 12 Jan 2018 15:46:47 +0100
Johan Hovold  wrote:

> On Tue, Jan 09, 2018 at 06:43:47PM +0100, Andreas Kemnade wrote:
> > On Fri, 22 Dec 2017 13:44:27 +0100
> > Johan Hovold  wrote:
> > 
> > [...]  
> > > I'd suggest reiterating the problem you're trying to solve and
> > > enumerating the previously discussed potential solutions in order to
> > > find a proper abstraction level for this (before getting lost in
> > > implementation details).
> > >   
> > The main point here is in short words: Having a device powered on or off
> > when the uart it is attached to, is used or not used anymore,
> > so the already available userspace applications do not need to be changed.  
> 
> So we'd end up with something in-between a kernel driver and a
> user-space solution. What about devices that need to be (partially)
> powered also when the port isn't open? A pure user-space solution would
> be able to handle all variants.
> 
Well partly powered devices are at many places, And they hide that problem
from userspace, just get the open()/get() and close()/put() from there and 
power the
device accordingly. 

So the question still remains why should the kernel hide some things and some
it should not.
If it all is in userspace, then there is still something needed in the 
devicetree
(if I understand correctly, every information about hardware which cannot be
auto-probed belongs into device tree) so that the userspace knows what kind of
device is at that port. So there can be a daemon powering on and off devices.
But that would break existing applications which just expect that they just need
to open/close the device. 

Or you need to have some inotify handler in userspace and attach it there to
react on close() and open() of that device.
But this thing needs to have two kind of information:

1. the type of chip available to do the right powerup sequence. 

2. how the chip is wired up to the cpu. 

So to avoid having hardware information spread all over the table at least
these information would need to be in devicetree. But that also all feels
like a hack and hard to maintain.

Regards,
Andreas


pgpUTBsCJ8UuT.pgp
Description: OpenPGP digital signature

Re: [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Hi Johan,

> Am 12.01.2018 um 16:39 schrieb Johan Hovold :
> 
>> Let's restart this discussion and focus on the main roadblock (others
>> are minor details which can be sorted out later).
>> 
>> If it feels like a hack, the key issue seems to me to be the choice of
>> the API to present the GPS data to user space. Right?
> 
> Or even more fundamentally, does this belong in the kernel at all?

Yes, that can be questioned of course. It was questioned and discussed
several times and I thought the answer was a clear yes. But let's reiterate.

> 
> Also it seems at least part of your specific problem is that you have
> failed to wire up the WAKEUP pin of the W2SG0004/84 properly,

The w2sg0004 has no wakeup pin. At least I can't find one in the data sheet.

The two pins you refer to from the 0084 data sheet are called BootSelect0/1
in the 0004 and have a different function.

To be clear, we did not fail to wire it up. We did the design before the
0084 was announced and available. We just had to swap in the 0084 into
existing PCBs during production because the 0004 became EOL. Otherwise
we would probably still use the 0004 without WAKEUP output.

To make it worse, we have no documentation for an individual board if
an 0004 or 0084 chip is installed and there is no means how a software
can find out which one it is talking to (especially before properly
powering on). Therefore we can not even provide two different device
trees or drivers or whatever, unless we ask people to open their device
and look on the chip. Quite crazy wrt. user-friendlyness of software
installation in 2018...

Therefore, a driver must be capable to handle both chips in the same way,
with minimalistic assumptions, even if the 0084 could provide a direct
signal to make it easier than using serdev to monitor the data stream.

>  which then
> forces you to look at the data stream to determine the power state of
> the chip. Judging from a quick look at the GTA04 schematics it seems
> you've even connected the WAKEUP output to the 1V8_OUT output?!

No. You failed to see that this is an optional 0R, which is not installed.
The 0R on pin 7 (BootSelect1) to GND was removed when we did switch from
0004 to 0084. Pin 6 (BootSelect0/WAKEUP) was never connected.

> The kernel is probably not the place to be working around issues like
> that,

You appear to assume this our only motivation is to make a workaround for
a hardware design flaw but that isn't.

The purpose of the driver is to provide power management for the GPS
subsystem which happens to be based on a chip with limited functionality.

And the serdev thing is the solution, not the requirement...

> even if serdev at least allows for such hacks to be fairly
> isolated in drivers (unlike some of the earlier proposals touching core
> code).

Please tell me why there are so many hacks for hardware issues in certain
drivers. Any why those are good and this one (if it is one at all) is not.

Some picks random fgrep -iR hack drivers

drivers/char/random.c: * Hack to deal with crazy userspace progams when they 
are all trying
drivers/clk/meson/meson8b.c: * a new clk_hw, and this hack will no longer 
work. Releasing the ccr
drivers/clk/samsung/clk-exynos3250.c:   /* HACK: fin_pll hardcoded to xusbxti 
until detection is implemented. */
drivers/gpu/drm/amd/amdkfd/kfd_events.c: * This hack is wrong, but 
nobody is likely to notice.
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c:   * HACK: IGT 
tests expect that each plane can only have one
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c:  /* It's a hack for s3 
since in 4.9 kernel filter out cursor buffer
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c:  /* TODO This 
hack should go away */
drivers/gpu/drm/amd/display/dc/core/dc_link.c:  /* A hack to avoid failing any 
modes for EDID override feature on

What I can learn from your discussion is that it might be considerable
to add an optional gpio for the 0084 WAKEUP and add some logic to
support users who have or will have that pin connected.

But even then we would need a driver to handle this gpio and issue
an on/off impulse on the other to switch states. It would be a different
driver (variant - maybe some CONFIG option or handled by code), but not
"no driver".

> 
>> I see three reasonable options how this presentation can be done:
>> 
>> 1. char device
>> 2. tty device
>> 3. some new gps interface API (similar to network, bluetooth interfaces)
>> 4. no driver and use the UART tty directly
>> 
>> Pros and cons:
> 
>> 4. no driver and use UART directly
>> + a non-solution seems to be attractive
>> - must turn on/off chip by gpio hacks from user-space
> 
> I'm not sure that would amount to more of hack then doing it in the
> kernel would.

It might not be big effort in the user-space code/scripts.

But much effort to convince all the plethora of user-space client maintainers
to integrate something. And have them roll out. And have 

Re: [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Hi Johan,

> Am 12.01.2018 um 16:39 schrieb Johan Hovold :
> 
>> Let's restart this discussion and focus on the main roadblock (others
>> are minor details which can be sorted out later).
>> 
>> If it feels like a hack, the key issue seems to me to be the choice of
>> the API to present the GPS data to user space. Right?
> 
> Or even more fundamentally, does this belong in the kernel at all?

Yes, that can be questioned of course. It was questioned and discussed
several times and I thought the answer was a clear yes. But let's reiterate.

> 
> Also it seems at least part of your specific problem is that you have
> failed to wire up the WAKEUP pin of the W2SG0004/84 properly,

The w2sg0004 has no wakeup pin. At least I can't find one in the data sheet.

The two pins you refer to from the 0084 data sheet are called BootSelect0/1
in the 0004 and have a different function.

To be clear, we did not fail to wire it up. We did the design before the
0084 was announced and available. We just had to swap in the 0084 into
existing PCBs during production because the 0004 became EOL. Otherwise
we would probably still use the 0004 without WAKEUP output.

To make it worse, we have no documentation for an individual board if
an 0004 or 0084 chip is installed and there is no means how a software
can find out which one it is talking to (especially before properly
powering on). Therefore we can not even provide two different device
trees or drivers or whatever, unless we ask people to open their device
and look on the chip. Quite crazy wrt. user-friendlyness of software
installation in 2018...

Therefore, a driver must be capable to handle both chips in the same way,
with minimalistic assumptions, even if the 0084 could provide a direct
signal to make it easier than using serdev to monitor the data stream.

>  which then
> forces you to look at the data stream to determine the power state of
> the chip. Judging from a quick look at the GTA04 schematics it seems
> you've even connected the WAKEUP output to the 1V8_OUT output?!

No. You failed to see that this is an optional 0R, which is not installed.
The 0R on pin 7 (BootSelect1) to GND was removed when we did switch from
0004 to 0084. Pin 6 (BootSelect0/WAKEUP) was never connected.

> The kernel is probably not the place to be working around issues like
> that,

You appear to assume this our only motivation is to make a workaround for
a hardware design flaw but that isn't.

The purpose of the driver is to provide power management for the GPS
subsystem which happens to be based on a chip with limited functionality.

And the serdev thing is the solution, not the requirement...

> even if serdev at least allows for such hacks to be fairly
> isolated in drivers (unlike some of the earlier proposals touching core
> code).

Please tell me why there are so many hacks for hardware issues in certain
drivers. Any why those are good and this one (if it is one at all) is not.

Some picks random fgrep -iR hack drivers

drivers/char/random.c: * Hack to deal with crazy userspace progams when they 
are all trying
drivers/clk/meson/meson8b.c: * a new clk_hw, and this hack will no longer 
work. Releasing the ccr
drivers/clk/samsung/clk-exynos3250.c:   /* HACK: fin_pll hardcoded to xusbxti 
until detection is implemented. */
drivers/gpu/drm/amd/amdkfd/kfd_events.c: * This hack is wrong, but 
nobody is likely to notice.
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c:   * HACK: IGT 
tests expect that each plane can only have one
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c:  /* It's a hack for s3 
since in 4.9 kernel filter out cursor buffer
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c:  /* TODO This 
hack should go away */
drivers/gpu/drm/amd/display/dc/core/dc_link.c:  /* A hack to avoid failing any 
modes for EDID override feature on

What I can learn from your discussion is that it might be considerable
to add an optional gpio for the 0084 WAKEUP and add some logic to
support users who have or will have that pin connected.

But even then we would need a driver to handle this gpio and issue
an on/off impulse on the other to switch states. It would be a different
driver (variant - maybe some CONFIG option or handled by code), but not
"no driver".

> 
>> I see three reasonable options how this presentation can be done:
>> 
>> 1. char device
>> 2. tty device
>> 3. some new gps interface API (similar to network, bluetooth interfaces)
>> 4. no driver and use the UART tty directly
>> 
>> Pros and cons:
> 
>> 4. no driver and use UART directly
>> + a non-solution seems to be attractive
>> - must turn on/off chip by gpio hacks from user-space
> 
> I'm not sure that would amount to more of hack then doing it in the
> kernel would.

It might not be big effort in the user-space code/scripts.

But much effort to convince all the plethora of user-space client maintainers
to integrate something. And have them roll out. And have distributions take it.

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Tue, Jan 09, 2018 at 12:55:11PM +0100, H. Nikolaus Schaller wrote:
> Hi Johan,
> 
> > Am 22.12.2017 um 15:40 schrieb H. Nikolaus Schaller :
> > 
> > Hi Johan,
> > 
> >> Am 22.12.2017 um 13:44 schrieb Johan Hovold :
> >> 
> >> On Fri, Dec 01, 2017 at 08:49:36AM +0100, H. Nikolaus Schaller wrote:
> >>> Add driver for Wi2Wi W2SG0004/84 GPS module connected to some SoC UART.
> >>> 
> >>> It uses serdev API hooks to monitor and forward the UART traffic to 
> >>> /dev/ttyGPSn
> >>> and turn on/off the module. It also detects if the module is turned on 
> >>> (sends data)
> >>> but should be off, e.g. if it was already turned on during boot or 
> >>> power-on-reset.
> >>> 
> >>> Additionally, rfkill block/unblock can be used to control an external LNA
> >>> (and power down the module if not needed).
> >>> 
> >>> The driver concept is based on code developed by Neil Brown 
> >>> 
> >>> but simplified and adapted to use the new serdev API introduced in v4.11.
> >> 
> >> I'm sorry (and I know this discussion has been going on for a long
> >> time),but this still feels like too much of a hack.
> 
> Happy new year ... Happy new attempt...

Same to you.

> Let's restart this discussion and focus on the main roadblock (others
> are minor details which can be sorted out later).
> 
> If it feels like a hack, the key issue seems to me to be the choice of
> the API to present the GPS data to user space. Right?

Or even more fundamentally, does this belong in the kernel at all?

Given that we'd still depend on gpsd and other, proprietary, daemons to
actually parse and use (also for control) the plethora of GPS protocols
available, it may even be best to just keep it all in user space.

The next user may want to keep the GPS powered also when the port is
closed; this all seems like policy that should remain in user space.

Now, if we'd ever have a proper GPS framework that handled everything in
kernel space (i.e. no more gpsd) then we would be able to write kernel
drivers that also take care of PM. But perhaps that's unlikely to ever
be realised given the state of things (proprietary protocols, numerous
quirky implementations, etc).

Also it seems at least part of your specific problem is that you have
failed to wire up the WAKEUP pin of the W2SG0004/84 properly, which then
forces you to look at the data stream to determine the power state of
the chip. Judging from a quick look at the GTA04 schematics it seems
you've even connected the WAKEUP output to the 1V8_OUT output?!

The kernel is probably not the place to be working around issues like
that, even if serdev at least allows for such hacks to be fairly
isolated in drivers (unlike some of the earlier proposals touching core
code).

> I see three reasonable options how this presentation can be done:
> 
> 1. char device
> 2. tty device
> 3. some new gps interface API (similar to network, bluetooth interfaces)
> 4. no driver and use the UART tty directly
> 
> Pros and cons:
 
> 4. no driver and use UART directly
> + a non-solution seems to be attractive
> - must turn on/off chip by gpio hacks from user-space

I'm not sure that would amount to more of hack then doing it in the
kernel would.

> - can not guarantee (!) to power off the chip if the last user-space
> process using it is killed (which is essential for power-management of
> a handheld, battery operated device)

That depends on how you implement things (extending gpsd, wrapper
script, pty daemon, ...).

> I would clearly prefer 3 over 2 over 1 over 4.
> 
> So do you see a chance that the kernel core team provides something useable
> (not perfect) for variant 3 in reasonable time (let's say 3-6 months)?

No, I'm afraid not. At least not if we're talking about a framework
that would replace gpsd.

> If not, I want to suggest to accept the second-best choice 2. for now and we
> will update the driver as soon as 3. appears. IMHO it would be a good test 
> case
> for a new subsystem.

Getting the interface right from the start is quite important, as
otherwise we may end up having to support a superseded one for a long
time.

Johan

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Tue, Jan 09, 2018 at 12:55:11PM +0100, H. Nikolaus Schaller wrote:
> Hi Johan,
> 
> > Am 22.12.2017 um 15:40 schrieb H. Nikolaus Schaller :
> > 
> > Hi Johan,
> > 
> >> Am 22.12.2017 um 13:44 schrieb Johan Hovold :
> >> 
> >> On Fri, Dec 01, 2017 at 08:49:36AM +0100, H. Nikolaus Schaller wrote:
> >>> Add driver for Wi2Wi W2SG0004/84 GPS module connected to some SoC UART.
> >>> 
> >>> It uses serdev API hooks to monitor and forward the UART traffic to 
> >>> /dev/ttyGPSn
> >>> and turn on/off the module. It also detects if the module is turned on 
> >>> (sends data)
> >>> but should be off, e.g. if it was already turned on during boot or 
> >>> power-on-reset.
> >>> 
> >>> Additionally, rfkill block/unblock can be used to control an external LNA
> >>> (and power down the module if not needed).
> >>> 
> >>> The driver concept is based on code developed by Neil Brown 
> >>> 
> >>> but simplified and adapted to use the new serdev API introduced in v4.11.
> >> 
> >> I'm sorry (and I know this discussion has been going on for a long
> >> time),but this still feels like too much of a hack.
> 
> Happy new year ... Happy new attempt...

Same to you.

> Let's restart this discussion and focus on the main roadblock (others
> are minor details which can be sorted out later).
> 
> If it feels like a hack, the key issue seems to me to be the choice of
> the API to present the GPS data to user space. Right?

Or even more fundamentally, does this belong in the kernel at all?

Given that we'd still depend on gpsd and other, proprietary, daemons to
actually parse and use (also for control) the plethora of GPS protocols
available, it may even be best to just keep it all in user space.

The next user may want to keep the GPS powered also when the port is
closed; this all seems like policy that should remain in user space.

Now, if we'd ever have a proper GPS framework that handled everything in
kernel space (i.e. no more gpsd) then we would be able to write kernel
drivers that also take care of PM. But perhaps that's unlikely to ever
be realised given the state of things (proprietary protocols, numerous
quirky implementations, etc).

Also it seems at least part of your specific problem is that you have
failed to wire up the WAKEUP pin of the W2SG0004/84 properly, which then
forces you to look at the data stream to determine the power state of
the chip. Judging from a quick look at the GTA04 schematics it seems
you've even connected the WAKEUP output to the 1V8_OUT output?!

The kernel is probably not the place to be working around issues like
that, even if serdev at least allows for such hacks to be fairly
isolated in drivers (unlike some of the earlier proposals touching core
code).

> I see three reasonable options how this presentation can be done:
> 
> 1. char device
> 2. tty device
> 3. some new gps interface API (similar to network, bluetooth interfaces)
> 4. no driver and use the UART tty directly
> 
> Pros and cons:
 
> 4. no driver and use UART directly
> + a non-solution seems to be attractive
> - must turn on/off chip by gpio hacks from user-space

I'm not sure that would amount to more of hack then doing it in the
kernel would.

> - can not guarantee (!) to power off the chip if the last user-space
> process using it is killed (which is essential for power-management of
> a handheld, battery operated device)

That depends on how you implement things (extending gpsd, wrapper
script, pty daemon, ...).

> I would clearly prefer 3 over 2 over 1 over 4.
> 
> So do you see a chance that the kernel core team provides something useable
> (not perfect) for variant 3 in reasonable time (let's say 3-6 months)?

No, I'm afraid not. At least not if we're talking about a framework
that would replace gpsd.

> If not, I want to suggest to accept the second-best choice 2. for now and we
> will update the driver as soon as 3. appears. IMHO it would be a good test 
> case
> for a new subsystem.

Getting the interface right from the start is quite important, as
otherwise we may end up having to support a superseded one for a long
time.

Johan

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Tue, Jan 09, 2018 at 06:43:47PM +0100, Andreas Kemnade wrote:
> On Fri, 22 Dec 2017 13:44:27 +0100
> Johan Hovold  wrote:
> 
> [...]
> > I'd suggest reiterating the problem you're trying to solve and
> > enumerating the previously discussed potential solutions in order to
> > find a proper abstraction level for this (before getting lost in
> > implementation details).
> > 
> The main point here is in short words: Having a device powered on or off
> when the uart it is attached to, is used or not used anymore,
> so the already available userspace applications do not need to be changed.

So we'd end up with something in-between a kernel driver and a
user-space solution. What about devices that need to be (partially)
powered also when the port isn't open? A pure user-space solution would
be able to handle all variants.

> I digged out a bit around:
> alternative aproaches were:
> adding hooks to the uart/tty layer:
> https://marc.info/?l=linux-kernel=14222014616=2
> https://marc.info/?l=devicetree=143130955414580=2

Thanks for the pointers, I remember those threads...

> I do not find it right now in my archive:
> adding a virtual gpio for dtr to the omap_serial driver.
> The driver behind the virtual io would then handle pm. One reason it was
> rejected was that the devicetree should only contain real hardware and
> not virtual stuff.

Oh, yeah, I think something like that made it in briefly before getting
reverted again.

I'll respond to Nikolaus mail as well.

Johan

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Tue, Jan 09, 2018 at 06:43:47PM +0100, Andreas Kemnade wrote:
> On Fri, 22 Dec 2017 13:44:27 +0100
> Johan Hovold  wrote:
> 
> [...]
> > I'd suggest reiterating the problem you're trying to solve and
> > enumerating the previously discussed potential solutions in order to
> > find a proper abstraction level for this (before getting lost in
> > implementation details).
> > 
> The main point here is in short words: Having a device powered on or off
> when the uart it is attached to, is used or not used anymore,
> so the already available userspace applications do not need to be changed.

So we'd end up with something in-between a kernel driver and a
user-space solution. What about devices that need to be (partially)
powered also when the port isn't open? A pure user-space solution would
be able to handle all variants.

> I digged out a bit around:
> alternative aproaches were:
> adding hooks to the uart/tty layer:
> https://marc.info/?l=linux-kernel=14222014616=2
> https://marc.info/?l=devicetree=143130955414580=2

Thanks for the pointers, I remember those threads...

> I do not find it right now in my archive:
> adding a virtual gpio for dtr to the omap_serial driver.
> The driver behind the virtual io would then handle pm. One reason it was
> rejected was that the devicetree should only contain real hardware and
> not virtual stuff.

Oh, yeah, I think something like that made it in briefly before getting
reverted again.

I'll respond to Nikolaus mail as well.

Johan

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Andreas Kemnade]

On Fri, 22 Dec 2017 13:44:27 +0100
Johan Hovold  wrote:

[...]
> I'd suggest reiterating the problem you're trying to solve and
> enumerating the previously discussed potential solutions in order to
> find a proper abstraction level for this (before getting lost in
> implementation details).
> 
The main point here is in short words: Having a device powered on or off
when the uart it is attached to, is used or not used anymore,
so the already available userspace applications do not need to be changed.

I digged out a bit around:
alternative aproaches were:
adding hooks to the uart/tty layer:
https://marc.info/?l=linux-kernel=14222014616=2
https://marc.info/?l=devicetree=143130955414580=2

I do not find it right now in my archive:
adding a virtual gpio for dtr to the omap_serial driver.
The driver behind the virtual io would then handle pm. One reason it was
rejected was that the devicetree should only contain real hardware and
not virtual stuff.

Regards,
Andreas


pgpa7BZ0bIL2w.pgp
Description: OpenPGP digital signature

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Andreas Kemnade]

On Fri, 22 Dec 2017 13:44:27 +0100
Johan Hovold  wrote:

[...]
> I'd suggest reiterating the problem you're trying to solve and
> enumerating the previously discussed potential solutions in order to
> find a proper abstraction level for this (before getting lost in
> implementation details).
> 
The main point here is in short words: Having a device powered on or off
when the uart it is attached to, is used or not used anymore,
so the already available userspace applications do not need to be changed.

I digged out a bit around:
alternative aproaches were:
adding hooks to the uart/tty layer:
https://marc.info/?l=linux-kernel=14222014616=2
https://marc.info/?l=devicetree=143130955414580=2

I do not find it right now in my archive:
adding a virtual gpio for dtr to the omap_serial driver.
The driver behind the virtual io would then handle pm. One reason it was
rejected was that the devicetree should only contain real hardware and
not virtual stuff.

Regards,
Andreas


pgpa7BZ0bIL2w.pgp
Description: OpenPGP digital signature

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Hi Johan,

> Am 22.12.2017 um 15:40 schrieb H. Nikolaus Schaller :
> 
> Hi Johan,
> 
>> Am 22.12.2017 um 13:44 schrieb Johan Hovold :
>> 
>> On Fri, Dec 01, 2017 at 08:49:36AM +0100, H. Nikolaus Schaller wrote:
>>> Add driver for Wi2Wi W2SG0004/84 GPS module connected to some SoC UART.
>>> 
>>> It uses serdev API hooks to monitor and forward the UART traffic to 
>>> /dev/ttyGPSn
>>> and turn on/off the module. It also detects if the module is turned on 
>>> (sends data)
>>> but should be off, e.g. if it was already turned on during boot or 
>>> power-on-reset.
>>> 
>>> Additionally, rfkill block/unblock can be used to control an external LNA
>>> (and power down the module if not needed).
>>> 
>>> The driver concept is based on code developed by Neil Brown 
>>> but simplified and adapted to use the new serdev API introduced in v4.11.
>> 
>> I'm sorry (and I know this discussion has been going on for a long
>> time),but this still feels like too much of a hack.

Happy new year ... Happy new attempt...

Let's restart this discussion and focus on the main roadblock (others are minor
details which can be sorted out later).

If it feels like a hack, the key issue seems to me to be the choice of
the API to present the GPS data to user space. Right?

I see three reasonable options how this presentation can be done:

1. char device
2. tty device
3. some new gps interface API (similar to network, bluetooth interfaces)
4. no driver and use the UART tty directly

Pros and cons:

1. char device
+ seems to save resources (but IMHO doesn't if we look deeper to handle select, 
blocking, buffer overflow)
- the standard function of buffering a character stream has to be done by this 
driver again, although tty subsystem already has proper buffering
- no line disciplines (e.g. if some gps client wants to translate CR and NL or 
use canonical/noncanonical mode)
- capabilities of the interface change if same chip is connected through USB or 
Bluetooth serial interface

2. tty device
+ full tty port like USB, Bluetooth or UART connection (w/o driver)
+ handles tcsetattr like USB, Bluetooth or UART
+ buffering and line disciplines come for free (at least wrt. driver code)
+ tested
- seems to appear to be complex and overkill and a hack (but IMHO is neither)

3. some new gps interface API
+ could become very elegant and general
- does not exist (AFAIK not even a plan but I am not aware of everything)
- no user-space daemons and applications exist which use it

4. no driver and use UART directly
+ a non-solution seems to be attractive
- must turn on/off chip by gpio hacks from user-space
- can not guarantee (!) to power off the chip if the last user-space process 
using it is killed
  (which is essential for power-management of a handheld, battery operated 
device)

I would clearly prefer 3 over 2 over 1 over 4.

So do you see a chance that the kernel core team provides something useable
(not perfect) for variant 3 in reasonable time (let's say 3-6 months)?

If not, I want to suggest to accept the second-best choice 2. for now and we
will update the driver as soon as 3. appears. IMHO it would be a good test case
for a new subsystem.

Please advise how you want to proceed.

BR and thanks,
Nikolaus

Re: [Letux-kernel] [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Hi Johan,

> Am 22.12.2017 um 15:40 schrieb H. Nikolaus Schaller :
> 
> Hi Johan,
> 
>> Am 22.12.2017 um 13:44 schrieb Johan Hovold :
>> 
>> On Fri, Dec 01, 2017 at 08:49:36AM +0100, H. Nikolaus Schaller wrote:
>>> Add driver for Wi2Wi W2SG0004/84 GPS module connected to some SoC UART.
>>> 
>>> It uses serdev API hooks to monitor and forward the UART traffic to 
>>> /dev/ttyGPSn
>>> and turn on/off the module. It also detects if the module is turned on 
>>> (sends data)
>>> but should be off, e.g. if it was already turned on during boot or 
>>> power-on-reset.
>>> 
>>> Additionally, rfkill block/unblock can be used to control an external LNA
>>> (and power down the module if not needed).
>>> 
>>> The driver concept is based on code developed by Neil Brown 
>>> but simplified and adapted to use the new serdev API introduced in v4.11.
>> 
>> I'm sorry (and I know this discussion has been going on for a long
>> time),but this still feels like too much of a hack.

Happy new year ... Happy new attempt...

Let's restart this discussion and focus on the main roadblock (others are minor
details which can be sorted out later).

If it feels like a hack, the key issue seems to me to be the choice of
the API to present the GPS data to user space. Right?

I see three reasonable options how this presentation can be done:

1. char device
2. tty device
3. some new gps interface API (similar to network, bluetooth interfaces)
4. no driver and use the UART tty directly

Pros and cons:

1. char device
+ seems to save resources (but IMHO doesn't if we look deeper to handle select, 
blocking, buffer overflow)
- the standard function of buffering a character stream has to be done by this 
driver again, although tty subsystem already has proper buffering
- no line disciplines (e.g. if some gps client wants to translate CR and NL or 
use canonical/noncanonical mode)
- capabilities of the interface change if same chip is connected through USB or 
Bluetooth serial interface

2. tty device
+ full tty port like USB, Bluetooth or UART connection (w/o driver)
+ handles tcsetattr like USB, Bluetooth or UART
+ buffering and line disciplines come for free (at least wrt. driver code)
+ tested
- seems to appear to be complex and overkill and a hack (but IMHO is neither)

3. some new gps interface API
+ could become very elegant and general
- does not exist (AFAIK not even a plan but I am not aware of everything)
- no user-space daemons and applications exist which use it

4. no driver and use UART directly
+ a non-solution seems to be attractive
- must turn on/off chip by gpio hacks from user-space
- can not guarantee (!) to power off the chip if the last user-space process 
using it is killed
  (which is essential for power-management of a handheld, battery operated 
device)

I would clearly prefer 3 over 2 over 1 over 4.

So do you see a chance that the kernel core team provides something useable
(not perfect) for variant 3 in reasonable time (let's say 3-6 months)?

If not, I want to suggest to accept the second-best choice 2. for now and we
will update the driver as soon as 3. appears. IMHO it would be a good test case
for a new subsystem.

Please advise how you want to proceed.

BR and thanks,
Nikolaus

Re: [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Hi Johan,

> Am 22.12.2017 um 13:44 schrieb Johan Hovold :
> 
> On Fri, Dec 01, 2017 at 08:49:36AM +0100, H. Nikolaus Schaller wrote:
>> Add driver for Wi2Wi W2SG0004/84 GPS module connected to some SoC UART.
>> 
>> It uses serdev API hooks to monitor and forward the UART traffic to 
>> /dev/ttyGPSn
>> and turn on/off the module. It also detects if the module is turned on 
>> (sends data)
>> but should be off, e.g. if it was already turned on during boot or 
>> power-on-reset.
>> 
>> Additionally, rfkill block/unblock can be used to control an external LNA
>> (and power down the module if not needed).
>> 
>> The driver concept is based on code developed by Neil Brown 
>> but simplified and adapted to use the new serdev API introduced in v4.11.
> 
> I'm sorry (and I know this discussion has been going on for a long
> time),

I'd say: already too much time.

> but this still feels like too much of a hack.

Well, to me it feels like review process is trying to get things 200% right
in the first step and therefore delays proposals that may already be useful
to real world users. Review is of course important to protect against severe
bugs and security issues.

My concern is that in 5 more years this chip is obsolete and then we never
had a working solution in distributions that base directly on kernel.org...

What I am lacking in this discussion is the spirit of starting with something
that basically works and permanently enhancing things. Like Linux started
25 years ago and many drivers look very different in v4.15 than v2.6.32.

Instead, we are sent back every time to rework it completely and at some point
our enthusiasm (and time budget) has boiled down to 0 because we see no more
reward for working on this.

> 
> You're registering a tty driver to allow user space to continue treat
> this as a tty device, but you provide no means of actually modifying
> anything (line settings, etc).

That was planned for a second step but is not important for pure GPS
reception.

> It's essentially just a character device
> with common tty ioctls as noops from a device PoV (well, plus the ldisc
> buffering and processing).

Yes. The buffering is the more important aspect and as far as I understand
we would have to implement our own buffer for a chardev driver. Buffering is
perfectly solved for tty devices.

Another aspect is that the same chip connected through an USB or Bluetooth
connection is presented as a tty device and not a char dev.

> This will probably require someone to first implement a generic gps
> framework with a properly defined interface which you may then teach
> gpsd to use (e.g. to avoid all its autodetection functionality) instead.

Yes, that is what I dream of.

But in past 5 years there was no "someone" to pop up and my time to work
on this topic is too limited. It is not even my main focus of efforts.

So I prefer solutions that can be done today with today's means and not
dreams (even if we share them).

> Or some entirely different approach, for example, where you manage
> everything from user space.

> 
> I'd suggest reiterating the problem you're trying to solve and
> enumerating the previously discussed potential solutions in order to
> find a proper abstraction level for this (before getting lost in
> implementation details).

Yes, please feel free to write patches that implement it that way.

> 
> That being said, I'm still pointing some bugs and issue below that you
> can consider for future versions of this (and other drivers) below.

Thanks!

> 
>> Signed-off-by: H. Nikolaus Schaller 
>> ---
>> drivers/misc/Kconfig|  10 +
>> drivers/misc/Makefile   |   1 +
>> drivers/misc/w2sg0004.c | 553 
>> 
>> 3 files changed, 564 insertions(+)
>> create mode 100644 drivers/misc/w2sg0004.c
>> 
>> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
>> index f1a5c2357b14..a3b11016ed2b 100644
>> --- a/drivers/misc/Kconfig
>> +++ b/drivers/misc/Kconfig
>> @@ -508,4 +508,14 @@ source "drivers/misc/mic/Kconfig"
>> source "drivers/misc/genwqe/Kconfig"
>> source "drivers/misc/echo/Kconfig"
>> source "drivers/misc/cxl/Kconfig"
>> +
>> +config W2SG0004
>> +tristate "W2SG00x4 on/off control"
> 
> Please provide a better summary for what this driver does.

Ok.

> 
>> +depends on GPIOLIB && SERIAL_DEV_BUS
>> +help
>> +  Enable on/off control of W2SG00x4 GPS moduled connected

s/moduled/module/

> 
> Some whitespace issue here.

Ok.

> 
>> +  to some SoC UART to allow powering up/down if the /dev/ttyGPSn
>> +  is opened/closed.
>> +  It also provides a rfkill gps name to control the LNA power.
>> +
>> endmenu
>> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
>> index 5ca5f64df478..d9d824b3d20a 100644
>> --- a/drivers/misc/Makefile
>> +++ b/drivers/misc/Makefile
>> @@ -50,6 +50,7 @@ obj-$(CONFIG_SRAM_EXEC)+= sram-exec.o
>> obj-y   

Re: [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Hi Johan,

> Am 22.12.2017 um 13:44 schrieb Johan Hovold :
> 
> On Fri, Dec 01, 2017 at 08:49:36AM +0100, H. Nikolaus Schaller wrote:
>> Add driver for Wi2Wi W2SG0004/84 GPS module connected to some SoC UART.
>> 
>> It uses serdev API hooks to monitor and forward the UART traffic to 
>> /dev/ttyGPSn
>> and turn on/off the module. It also detects if the module is turned on 
>> (sends data)
>> but should be off, e.g. if it was already turned on during boot or 
>> power-on-reset.
>> 
>> Additionally, rfkill block/unblock can be used to control an external LNA
>> (and power down the module if not needed).
>> 
>> The driver concept is based on code developed by Neil Brown 
>> but simplified and adapted to use the new serdev API introduced in v4.11.
> 
> I'm sorry (and I know this discussion has been going on for a long
> time),

I'd say: already too much time.

> but this still feels like too much of a hack.

Well, to me it feels like review process is trying to get things 200% right
in the first step and therefore delays proposals that may already be useful
to real world users. Review is of course important to protect against severe
bugs and security issues.

My concern is that in 5 more years this chip is obsolete and then we never
had a working solution in distributions that base directly on kernel.org...

What I am lacking in this discussion is the spirit of starting with something
that basically works and permanently enhancing things. Like Linux started
25 years ago and many drivers look very different in v4.15 than v2.6.32.

Instead, we are sent back every time to rework it completely and at some point
our enthusiasm (and time budget) has boiled down to 0 because we see no more
reward for working on this.

> 
> You're registering a tty driver to allow user space to continue treat
> this as a tty device, but you provide no means of actually modifying
> anything (line settings, etc).

That was planned for a second step but is not important for pure GPS
reception.

> It's essentially just a character device
> with common tty ioctls as noops from a device PoV (well, plus the ldisc
> buffering and processing).

Yes. The buffering is the more important aspect and as far as I understand
we would have to implement our own buffer for a chardev driver. Buffering is
perfectly solved for tty devices.

Another aspect is that the same chip connected through an USB or Bluetooth
connection is presented as a tty device and not a char dev.

> This will probably require someone to first implement a generic gps
> framework with a properly defined interface which you may then teach
> gpsd to use (e.g. to avoid all its autodetection functionality) instead.

Yes, that is what I dream of.

But in past 5 years there was no "someone" to pop up and my time to work
on this topic is too limited. It is not even my main focus of efforts.

So I prefer solutions that can be done today with today's means and not
dreams (even if we share them).

> Or some entirely different approach, for example, where you manage
> everything from user space.

> 
> I'd suggest reiterating the problem you're trying to solve and
> enumerating the previously discussed potential solutions in order to
> find a proper abstraction level for this (before getting lost in
> implementation details).

Yes, please feel free to write patches that implement it that way.

> 
> That being said, I'm still pointing some bugs and issue below that you
> can consider for future versions of this (and other drivers) below.

Thanks!

> 
>> Signed-off-by: H. Nikolaus Schaller 
>> ---
>> drivers/misc/Kconfig|  10 +
>> drivers/misc/Makefile   |   1 +
>> drivers/misc/w2sg0004.c | 553 
>> 
>> 3 files changed, 564 insertions(+)
>> create mode 100644 drivers/misc/w2sg0004.c
>> 
>> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
>> index f1a5c2357b14..a3b11016ed2b 100644
>> --- a/drivers/misc/Kconfig
>> +++ b/drivers/misc/Kconfig
>> @@ -508,4 +508,14 @@ source "drivers/misc/mic/Kconfig"
>> source "drivers/misc/genwqe/Kconfig"
>> source "drivers/misc/echo/Kconfig"
>> source "drivers/misc/cxl/Kconfig"
>> +
>> +config W2SG0004
>> +tristate "W2SG00x4 on/off control"
> 
> Please provide a better summary for what this driver does.

Ok.

> 
>> +depends on GPIOLIB && SERIAL_DEV_BUS
>> +help
>> +  Enable on/off control of W2SG00x4 GPS moduled connected

s/moduled/module/

> 
> Some whitespace issue here.

Ok.

> 
>> +  to some SoC UART to allow powering up/down if the /dev/ttyGPSn
>> +  is opened/closed.
>> +  It also provides a rfkill gps name to control the LNA power.
>> +
>> endmenu
>> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
>> index 5ca5f64df478..d9d824b3d20a 100644
>> --- a/drivers/misc/Makefile
>> +++ b/drivers/misc/Makefile
>> @@ -50,6 +50,7 @@ obj-$(CONFIG_SRAM_EXEC)+= sram-exec.o
>> obj-y+= mic/
>> obj-$(CONFIG_GENWQE) += 

Re: [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Fri, Dec 01, 2017 at 08:49:36AM +0100, H. Nikolaus Schaller wrote:
> Add driver for Wi2Wi W2SG0004/84 GPS module connected to some SoC UART.
> 
> It uses serdev API hooks to monitor and forward the UART traffic to 
> /dev/ttyGPSn
> and turn on/off the module. It also detects if the module is turned on (sends 
> data)
> but should be off, e.g. if it was already turned on during boot or 
> power-on-reset.
> 
> Additionally, rfkill block/unblock can be used to control an external LNA
> (and power down the module if not needed).
> 
> The driver concept is based on code developed by Neil Brown 
> but simplified and adapted to use the new serdev API introduced in v4.11.

I'm sorry (and I know this discussion has been going on for a long
time), but this still feels like too much of a hack.

You're registering a tty driver to allow user space to continue treat
this as a tty device, but you provide no means of actually modifying
anything (line settings, etc). It's essentially just a character device
with common tty ioctls as noops from a device PoV (well, plus the ldisc
buffering and processing).

This will probably require someone to first implement a generic gps
framework with a properly defined interface which you may then teach
gpsd to use (e.g. to avoid all its autodetection functionality) instead.

Or some entirely different approach, for example, where you manage
everything from user space.

I'd suggest reiterating the problem you're trying to solve and
enumerating the previously discussed potential solutions in order to
find a proper abstraction level for this (before getting lost in
implementation details).

That being said, I'm still pointing some bugs and issue below that you
can consider for future versions of this (and other drivers) below.

> Signed-off-by: H. Nikolaus Schaller 
> ---
>  drivers/misc/Kconfig|  10 +
>  drivers/misc/Makefile   |   1 +
>  drivers/misc/w2sg0004.c | 553 
> 
>  3 files changed, 564 insertions(+)
>  create mode 100644 drivers/misc/w2sg0004.c
> 
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index f1a5c2357b14..a3b11016ed2b 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -508,4 +508,14 @@ source "drivers/misc/mic/Kconfig"
>  source "drivers/misc/genwqe/Kconfig"
>  source "drivers/misc/echo/Kconfig"
>  source "drivers/misc/cxl/Kconfig"
> +
> +config W2SG0004
> + tristate "W2SG00x4 on/off control"

Please provide a better summary for what this driver does.

> + depends on GPIOLIB && SERIAL_DEV_BUS
> + help
> +  Enable on/off control of W2SG00x4 GPS moduled connected

Some whitespace issue here.

> +   to some SoC UART to allow powering up/down if the /dev/ttyGPSn
> +   is opened/closed.
> +   It also provides a rfkill gps name to control the LNA power.
> +
>  endmenu
> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> index 5ca5f64df478..d9d824b3d20a 100644
> --- a/drivers/misc/Makefile
> +++ b/drivers/misc/Makefile
> @@ -50,6 +50,7 @@ obj-$(CONFIG_SRAM_EXEC) += sram-exec.o
>  obj-y+= mic/
>  obj-$(CONFIG_GENWQE) += genwqe/
>  obj-$(CONFIG_ECHO)   += echo/
> +obj-$(CONFIG_W2SG0004)   += w2sg0004.o
>  obj-$(CONFIG_VEXPRESS_SYSCFG)+= vexpress-syscfg.o
>  obj-$(CONFIG_CXL_BASE)   += cxl/
>  obj-$(CONFIG_ASPEED_LPC_CTRL)+= aspeed-lpc-ctrl.o
> diff --git a/drivers/misc/w2sg0004.c b/drivers/misc/w2sg0004.c
> new file mode 100644
> index ..6bfd12eb8e02
> --- /dev/null
> +++ b/drivers/misc/w2sg0004.c
> @@ -0,0 +1,553 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Driver for power controlling the w2sg0004/w2sg0084 GPS receiver.
> + *
> + * Copyright (C) 2013 Neil Brown 
> + * Copyright (C) 2015-2017 H. Nikolaus Schaller ,
> + *   Golden Delicious Computers
> + *
> + * This receiver has an ON/OFF pin which must be toggled to
> + * turn the device 'on' of 'off'.  A high->low->high toggle

s/of/or/

> + * will switch the device on if it is off, and off if it is on.
> + *
> + * To enable receiving on/off requests we register with the
> + * UART power management notifications.

No, the UART (serial device) would be the grandparent of your serdev
device (for which you register PM callbacks).

> + *
> + * It is not possible to directly detect the state of the device.

Didn't the 0084 version have a pin for this?

> + * However when it is on it will send characters on a UART line
> + * regularly.
> + *
> + * To detect that the power state is out of sync (e.g. if GPS
> + * was enabled before a reboot), we register for UART data received
> + * notifications.
> + *
> + * In addition we register as a rfkill client so that we can
> + * control the LNA power.
> + *
> + */
> +
> +#include 
> +#include 
> +#include 
> +#include 
> +#include 
> 

Re: [PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[Johan Hovold]

On Fri, Dec 01, 2017 at 08:49:36AM +0100, H. Nikolaus Schaller wrote:
> Add driver for Wi2Wi W2SG0004/84 GPS module connected to some SoC UART.
> 
> It uses serdev API hooks to monitor and forward the UART traffic to 
> /dev/ttyGPSn
> and turn on/off the module. It also detects if the module is turned on (sends 
> data)
> but should be off, e.g. if it was already turned on during boot or 
> power-on-reset.
> 
> Additionally, rfkill block/unblock can be used to control an external LNA
> (and power down the module if not needed).
> 
> The driver concept is based on code developed by Neil Brown 
> but simplified and adapted to use the new serdev API introduced in v4.11.

I'm sorry (and I know this discussion has been going on for a long
time), but this still feels like too much of a hack.

You're registering a tty driver to allow user space to continue treat
this as a tty device, but you provide no means of actually modifying
anything (line settings, etc). It's essentially just a character device
with common tty ioctls as noops from a device PoV (well, plus the ldisc
buffering and processing).

This will probably require someone to first implement a generic gps
framework with a properly defined interface which you may then teach
gpsd to use (e.g. to avoid all its autodetection functionality) instead.

Or some entirely different approach, for example, where you manage
everything from user space.

I'd suggest reiterating the problem you're trying to solve and
enumerating the previously discussed potential solutions in order to
find a proper abstraction level for this (before getting lost in
implementation details).

That being said, I'm still pointing some bugs and issue below that you
can consider for future versions of this (and other drivers) below.

> Signed-off-by: H. Nikolaus Schaller 
> ---
>  drivers/misc/Kconfig|  10 +
>  drivers/misc/Makefile   |   1 +
>  drivers/misc/w2sg0004.c | 553 
> 
>  3 files changed, 564 insertions(+)
>  create mode 100644 drivers/misc/w2sg0004.c
> 
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index f1a5c2357b14..a3b11016ed2b 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -508,4 +508,14 @@ source "drivers/misc/mic/Kconfig"
>  source "drivers/misc/genwqe/Kconfig"
>  source "drivers/misc/echo/Kconfig"
>  source "drivers/misc/cxl/Kconfig"
> +
> +config W2SG0004
> + tristate "W2SG00x4 on/off control"

Please provide a better summary for what this driver does.

> + depends on GPIOLIB && SERIAL_DEV_BUS
> + help
> +  Enable on/off control of W2SG00x4 GPS moduled connected

Some whitespace issue here.

> +   to some SoC UART to allow powering up/down if the /dev/ttyGPSn
> +   is opened/closed.
> +   It also provides a rfkill gps name to control the LNA power.
> +
>  endmenu
> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> index 5ca5f64df478..d9d824b3d20a 100644
> --- a/drivers/misc/Makefile
> +++ b/drivers/misc/Makefile
> @@ -50,6 +50,7 @@ obj-$(CONFIG_SRAM_EXEC) += sram-exec.o
>  obj-y+= mic/
>  obj-$(CONFIG_GENWQE) += genwqe/
>  obj-$(CONFIG_ECHO)   += echo/
> +obj-$(CONFIG_W2SG0004)   += w2sg0004.o
>  obj-$(CONFIG_VEXPRESS_SYSCFG)+= vexpress-syscfg.o
>  obj-$(CONFIG_CXL_BASE)   += cxl/
>  obj-$(CONFIG_ASPEED_LPC_CTRL)+= aspeed-lpc-ctrl.o
> diff --git a/drivers/misc/w2sg0004.c b/drivers/misc/w2sg0004.c
> new file mode 100644
> index ..6bfd12eb8e02
> --- /dev/null
> +++ b/drivers/misc/w2sg0004.c
> @@ -0,0 +1,553 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Driver for power controlling the w2sg0004/w2sg0084 GPS receiver.
> + *
> + * Copyright (C) 2013 Neil Brown 
> + * Copyright (C) 2015-2017 H. Nikolaus Schaller ,
> + *   Golden Delicious Computers
> + *
> + * This receiver has an ON/OFF pin which must be toggled to
> + * turn the device 'on' of 'off'.  A high->low->high toggle

s/of/or/

> + * will switch the device on if it is off, and off if it is on.
> + *
> + * To enable receiving on/off requests we register with the
> + * UART power management notifications.

No, the UART (serial device) would be the grandparent of your serdev
device (for which you register PM callbacks).

> + *
> + * It is not possible to directly detect the state of the device.

Didn't the 0084 version have a pin for this?

> + * However when it is on it will send characters on a UART line
> + * regularly.
> + *
> + * To detect that the power state is out of sync (e.g. if GPS
> + * was enabled before a reboot), we register for UART data received
> + * notifications.
> + *
> + * In addition we register as a rfkill client so that we can
> + * control the LNA power.
> + *
> + */
> +
> +#include 
> +#include 
> +#include 
> +#include 
> +#include 
> +#include 
> +#include 
> +#include 
> +#include 
> +#include 
> 

[PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Add driver for Wi2Wi W2SG0004/84 GPS module connected to some SoC UART.

It uses serdev API hooks to monitor and forward the UART traffic to /dev/ttyGPSn
and turn on/off the module. It also detects if the module is turned on (sends 
data)
but should be off, e.g. if it was already turned on during boot or 
power-on-reset.

Additionally, rfkill block/unblock can be used to control an external LNA
(and power down the module if not needed).

The driver concept is based on code developed by Neil Brown 
but simplified and adapted to use the new serdev API introduced in v4.11.

Signed-off-by: H. Nikolaus Schaller 
---
 drivers/misc/Kconfig|  10 +
 drivers/misc/Makefile   |   1 +
 drivers/misc/w2sg0004.c | 553 
 3 files changed, 564 insertions(+)
 create mode 100644 drivers/misc/w2sg0004.c

diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index f1a5c2357b14..a3b11016ed2b 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -508,4 +508,14 @@ source "drivers/misc/mic/Kconfig"
 source "drivers/misc/genwqe/Kconfig"
 source "drivers/misc/echo/Kconfig"
 source "drivers/misc/cxl/Kconfig"
+
+config W2SG0004
+   tristate "W2SG00x4 on/off control"
+   depends on GPIOLIB && SERIAL_DEV_BUS
+   help
+  Enable on/off control of W2SG00x4 GPS moduled connected
+ to some SoC UART to allow powering up/down if the /dev/ttyGPSn
+ is opened/closed.
+ It also provides a rfkill gps name to control the LNA power.
+
 endmenu
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index 5ca5f64df478..d9d824b3d20a 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -50,6 +50,7 @@ obj-$(CONFIG_SRAM_EXEC)   += sram-exec.o
 obj-y  += mic/
 obj-$(CONFIG_GENWQE)   += genwqe/
 obj-$(CONFIG_ECHO) += echo/
+obj-$(CONFIG_W2SG0004) += w2sg0004.o
 obj-$(CONFIG_VEXPRESS_SYSCFG)  += vexpress-syscfg.o
 obj-$(CONFIG_CXL_BASE) += cxl/
 obj-$(CONFIG_ASPEED_LPC_CTRL)  += aspeed-lpc-ctrl.o
diff --git a/drivers/misc/w2sg0004.c b/drivers/misc/w2sg0004.c
new file mode 100644
index ..6bfd12eb8e02
--- /dev/null
+++ b/drivers/misc/w2sg0004.c
@@ -0,0 +1,553 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Driver for power controlling the w2sg0004/w2sg0084 GPS receiver.
+ *
+ * Copyright (C) 2013 Neil Brown 
+ * Copyright (C) 2015-2017 H. Nikolaus Schaller ,
+ * Golden Delicious Computers
+ *
+ * This receiver has an ON/OFF pin which must be toggled to
+ * turn the device 'on' of 'off'.  A high->low->high toggle
+ * will switch the device on if it is off, and off if it is on.
+ *
+ * To enable receiving on/off requests we register with the
+ * UART power management notifications.
+ *
+ * It is not possible to directly detect the state of the device.
+ * However when it is on it will send characters on a UART line
+ * regularly.
+ *
+ * To detect that the power state is out of sync (e.g. if GPS
+ * was enabled before a reboot), we register for UART data received
+ * notifications.
+ *
+ * In addition we register as a rfkill client so that we can
+ * control the LNA power.
+ *
+ */
+
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+
+/*
+ * There seems to be restrictions on how quickly we can toggle the
+ * on/off line.  data sheets says "two rtc ticks", whatever that means.
+ * If we do it too soon it doesn't work.
+ * So we have a state machine which uses the common work queue to ensure
+ * clean transitions.
+ * When a change is requested we record that request and only act on it
+ * once the previous change has completed.
+ * A change involves a 10ms low pulse, and a 990ms raised level, so only
+ * one change per second.
+ */
+
+enum w2sg_state {
+   W2SG_IDLE,  /* is not changing state */
+   W2SG_PULSE, /* activate on/off impulse */
+   W2SG_NOPULSE/* deactivate on/off impulse */
+};
+
+struct w2sg_data {
+   struct  rfkill *rf_kill;
+   struct  regulator *lna_regulator;
+   int lna_blocked;/* rfkill block gps active */
+   int lna_is_off; /* LNA is currently off */
+   int is_on;  /* current state (0/1) */
+   unsigned long   last_toggle;
+   unsigned long   backoff;/* time to wait since last_toggle */
+   int on_off_gpio;/* the on-off gpio number */
+   struct  serdev_device *uart;/* uart connected to the chip */
+   struct  tty_driver *tty_drv;/* this is the user space tty */
+   struct  device *dev;/* from tty_port_register_device() */
+   struct  tty_port port;
+   int 

[PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Add driver for Wi2Wi W2SG0004/84 GPS module connected to some SoC UART.

It uses serdev API hooks to monitor and forward the UART traffic to /dev/ttyGPSn
and turn on/off the module. It also detects if the module is turned on (sends 
data)
but should be off, e.g. if it was already turned on during boot or 
power-on-reset.

Additionally, rfkill block/unblock can be used to control an external LNA
(and power down the module if not needed).

The driver concept is based on code developed by Neil Brown 
but simplified and adapted to use the new serdev API introduced in v4.11.

Signed-off-by: H. Nikolaus Schaller 
---
 drivers/misc/Kconfig|  10 +
 drivers/misc/Makefile   |   1 +
 drivers/misc/w2sg0004.c | 553 
 3 files changed, 564 insertions(+)
 create mode 100644 drivers/misc/w2sg0004.c

diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index f1a5c2357b14..a3b11016ed2b 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -508,4 +508,14 @@ source "drivers/misc/mic/Kconfig"
 source "drivers/misc/genwqe/Kconfig"
 source "drivers/misc/echo/Kconfig"
 source "drivers/misc/cxl/Kconfig"
+
+config W2SG0004
+   tristate "W2SG00x4 on/off control"
+   depends on GPIOLIB && SERIAL_DEV_BUS
+   help
+  Enable on/off control of W2SG00x4 GPS moduled connected
+ to some SoC UART to allow powering up/down if the /dev/ttyGPSn
+ is opened/closed.
+ It also provides a rfkill gps name to control the LNA power.
+
 endmenu
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index 5ca5f64df478..d9d824b3d20a 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -50,6 +50,7 @@ obj-$(CONFIG_SRAM_EXEC)   += sram-exec.o
 obj-y  += mic/
 obj-$(CONFIG_GENWQE)   += genwqe/
 obj-$(CONFIG_ECHO) += echo/
+obj-$(CONFIG_W2SG0004) += w2sg0004.o
 obj-$(CONFIG_VEXPRESS_SYSCFG)  += vexpress-syscfg.o
 obj-$(CONFIG_CXL_BASE) += cxl/
 obj-$(CONFIG_ASPEED_LPC_CTRL)  += aspeed-lpc-ctrl.o
diff --git a/drivers/misc/w2sg0004.c b/drivers/misc/w2sg0004.c
new file mode 100644
index ..6bfd12eb8e02
--- /dev/null
+++ b/drivers/misc/w2sg0004.c
@@ -0,0 +1,553 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Driver for power controlling the w2sg0004/w2sg0084 GPS receiver.
+ *
+ * Copyright (C) 2013 Neil Brown 
+ * Copyright (C) 2015-2017 H. Nikolaus Schaller ,
+ * Golden Delicious Computers
+ *
+ * This receiver has an ON/OFF pin which must be toggled to
+ * turn the device 'on' of 'off'.  A high->low->high toggle
+ * will switch the device on if it is off, and off if it is on.
+ *
+ * To enable receiving on/off requests we register with the
+ * UART power management notifications.
+ *
+ * It is not possible to directly detect the state of the device.
+ * However when it is on it will send characters on a UART line
+ * regularly.
+ *
+ * To detect that the power state is out of sync (e.g. if GPS
+ * was enabled before a reboot), we register for UART data received
+ * notifications.
+ *
+ * In addition we register as a rfkill client so that we can
+ * control the LNA power.
+ *
+ */
+
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+#include 
+
+/*
+ * There seems to be restrictions on how quickly we can toggle the
+ * on/off line.  data sheets says "two rtc ticks", whatever that means.
+ * If we do it too soon it doesn't work.
+ * So we have a state machine which uses the common work queue to ensure
+ * clean transitions.
+ * When a change is requested we record that request and only act on it
+ * once the previous change has completed.
+ * A change involves a 10ms low pulse, and a 990ms raised level, so only
+ * one change per second.
+ */
+
+enum w2sg_state {
+   W2SG_IDLE,  /* is not changing state */
+   W2SG_PULSE, /* activate on/off impulse */
+   W2SG_NOPULSE/* deactivate on/off impulse */
+};
+
+struct w2sg_data {
+   struct  rfkill *rf_kill;
+   struct  regulator *lna_regulator;
+   int lna_blocked;/* rfkill block gps active */
+   int lna_is_off; /* LNA is currently off */
+   int is_on;  /* current state (0/1) */
+   unsigned long   last_toggle;
+   unsigned long   backoff;/* time to wait since last_toggle */
+   int on_off_gpio;/* the on-off gpio number */
+   struct  serdev_device *uart;/* uart connected to the chip */
+   struct  tty_driver *tty_drv;/* this is the user space tty */
+   struct  device *dev;/* from tty_port_register_device() */
+   struct  tty_port port;
+   int open_count; /* how often we were opened */
+   enum