Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
On 05/19/2017 03:35 AM, Heikki Krogerus wrote: On Thu, May 18, 2017 at 02:08:53PM -0700, Badhri Jagan Sridharan wrote: On Thu, May 18, 2017 at 9:51 AM, Guenter Roeckwrote: On Thu, May 18, 2017 at 11:13:51AM +0200, Oliver Neukum wrote: Am Mittwoch, den 17.05.2017, 02:36 -0700 schrieb Guenter Roeck: On 05/17/2017 12:34 AM, Oliver Neukum wrote: Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan Sridharan: Hi, "Two independent set of mechanisms are defined to allow a USB Type-C DRP to functionally swap power and data roles. When USB PD is supported, power and data role swapping is performed as a subsequent step following the initial connection process. For non-PD implementations, power/data role swapping can optionally be dealt with as part of the initial connection process." Well, as I read it, without PD once a connection is established, you are stuck with your role. So it seems to me that blocking a later attempt to change it makes sense. That seems to be a harsh and not very user friendly reading of the specification. I would argue that the user doesn't care if the partner supports PD or not when selecting a role, and I would prefer to provide an implementation which is as user friendly as possible. Data role, no question, you are right. Power role is a different question. A switch of power role with PD should not lead to a disconnect. Any other method might. So equating them does not look like a good idea. Not really sure I can follow. If a partner does not support PD, there is no real distinction between data role and power role, or am I missing something ? Are you saying that, if a partner does not support PD, user space should request a data role swap instead, and that this would be acceptable for you ? I don't really understand the difference - a data role swap doesn't cause a disconnect either if the partner supports PD, and it would still result in a disconnect/reconnect sequence if the partner does not support PD - but if it works for you, fine with me. Badhri, would that work for us ? Yes Geunter that should work as well. Requesting non-pd role swap either through current_power_role or current_data_role is virtually the same. So if I understood this correctly, we'll skip this change, right? Yes. Thanks, Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
Am Donnerstag, den 18.05.2017, 14:08 -0700 schrieb Badhri Jagan Sridharan: > > Badhri, would that work for us ? > > Yes Geunter that should work as well. Requesting non-pd role swap either > through > current_power_role or current_data_role is virtually the same. Yes and that is the issue. If you can do PD and swap power roles, power roles will be swapped and data connection and driver assignments stay put. However without PD drivers will be unbound. That means that user space must be made aware that requesting a power role change will have side effects. Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
On Thu, May 18, 2017 at 02:08:53PM -0700, Badhri Jagan Sridharan wrote: > On Thu, May 18, 2017 at 9:51 AM, Guenter Roeckwrote: > > On Thu, May 18, 2017 at 11:13:51AM +0200, Oliver Neukum wrote: > >> Am Mittwoch, den 17.05.2017, 02:36 -0700 schrieb Guenter Roeck: > >> > On 05/17/2017 12:34 AM, Oliver Neukum wrote: > >> > > > >> > > Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan > >> > > Sridharan: > >> > > > >> > > Hi, > >> > > > >> > > > > >> > > > "Two independent set of mechanisms are defined to allow a USB Type-C > >> > > > DRP to functionally swap power and data roles. When USB PD is > >> > > > supported, power and data role swapping is performed as a subsequent > >> > > > step following the initial connection process. For non-PD > >> > > > implementations, > >> > > > power/data role swapping can optionally be dealt with as part of the > >> > > > initial > >> > > > connection process." > >> > > > >> > > Well, as I read it, without PD once a connection is established, you > >> > > are stuck with your role. So it seems to me that blocking a later > >> > > attempt to change it makes sense. > >> > > > >> > > >> > That seems to be a harsh and not very user friendly reading of the > >> > specification. > >> > > >> > I would argue that the user doesn't care if the partner supports PD or > >> > not > >> > when selecting a role, and I would prefer to provide an implementation > >> > which is > >> > as user friendly as possible. > >> > >> Data role, no question, you are right. > >> Power role is a different question. A switch of power role with PD should > >> not lead to a disconnect. Any other method might. So equating them does > >> not look like a good idea. > >> > > > > Not really sure I can follow. If a partner does not support PD, there is no > > real distinction between data role and power role, or am I missing > > something ? > > > > Are you saying that, if a partner does not support PD, user space should > > request a data role swap instead, and that this would be acceptable for you > > ? > > > > I don't really understand the difference - a data role swap doesn't cause > > a disconnect either if the partner supports PD, and it would still result > > in a disconnect/reconnect sequence if the partner does not support PD - > > but if it works for you, fine with me. > > > > Badhri, would that work for us ? > > Yes Geunter that should work as well. Requesting non-pd role swap either > through > current_power_role or current_data_role is virtually the same. So if I understood this correctly, we'll skip this change, right? Thanks, -- heikki -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
Not Sure whether my previous response was sent properly. So re-sending. On Thu, May 18, 2017 at 2:08 PM, Badhri Jagan Sridharanwrote: > On Thu, May 18, 2017 at 9:51 AM, Guenter Roeck wrote: >> On Thu, May 18, 2017 at 11:13:51AM +0200, Oliver Neukum wrote: >>> Am Mittwoch, den 17.05.2017, 02:36 -0700 schrieb Guenter Roeck: >>> > On 05/17/2017 12:34 AM, Oliver Neukum wrote: >>> > > >>> > > Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan >>> > > Sridharan: >>> > > >>> > > Hi, >>> > > >>> > > > >>> > > > "Two independent set of mechanisms are defined to allow a USB Type-C >>> > > > DRP to functionally swap power and data roles. When USB PD is >>> > > > supported, power and data role swapping is performed as a subsequent >>> > > > step following the initial connection process. For non-PD >>> > > > implementations, >>> > > > power/data role swapping can optionally be dealt with as part of the >>> > > > initial >>> > > > connection process." >>> > > >>> > > Well, as I read it, without PD once a connection is established, you >>> > > are stuck with your role. So it seems to me that blocking a later >>> > > attempt to change it makes sense. >>> > > >>> > >>> > That seems to be a harsh and not very user friendly reading of the >>> > specification. >>> > >>> > I would argue that the user doesn't care if the partner supports PD or not >>> > when selecting a role, and I would prefer to provide an implementation >>> > which is >>> > as user friendly as possible. >>> >>> Data role, no question, you are right. >>> Power role is a different question. A switch of power role with PD should >>> not lead to a disconnect. Any other method might. So equating them does >>> not look like a good idea. >>> >> >> Not really sure I can follow. If a partner does not support PD, there is no >> real distinction between data role and power role, or am I missing something >> ? >> >> Are you saying that, if a partner does not support PD, user space should >> request a data role swap instead, and that this would be acceptable for you ? >> >> I don't really understand the difference - a data role swap doesn't cause >> a disconnect either if the partner supports PD, and it would still result >> in a disconnect/reconnect sequence if the partner does not support PD - >> but if it works for you, fine with me. >> >> Badhri, would that work for us ? Yes Geunter that should work as well. Requesting non-pd role swap either through current_power_role or current_data_role is virtually the same. > > Yes Geunter that should work as well. Requesting non-pd role swap either > through > current_power_role or current_data_role is virtually the same. > >> >> Thanks, >> Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
On Thu, May 18, 2017 at 9:51 AM, Guenter Roeckwrote: > On Thu, May 18, 2017 at 11:13:51AM +0200, Oliver Neukum wrote: >> Am Mittwoch, den 17.05.2017, 02:36 -0700 schrieb Guenter Roeck: >> > On 05/17/2017 12:34 AM, Oliver Neukum wrote: >> > > >> > > Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan >> > > Sridharan: >> > > >> > > Hi, >> > > >> > > > >> > > > "Two independent set of mechanisms are defined to allow a USB Type-C >> > > > DRP to functionally swap power and data roles. When USB PD is >> > > > supported, power and data role swapping is performed as a subsequent >> > > > step following the initial connection process. For non-PD >> > > > implementations, >> > > > power/data role swapping can optionally be dealt with as part of the >> > > > initial >> > > > connection process." >> > > >> > > Well, as I read it, without PD once a connection is established, you >> > > are stuck with your role. So it seems to me that blocking a later >> > > attempt to change it makes sense. >> > > >> > >> > That seems to be a harsh and not very user friendly reading of the >> > specification. >> > >> > I would argue that the user doesn't care if the partner supports PD or not >> > when selecting a role, and I would prefer to provide an implementation >> > which is >> > as user friendly as possible. >> >> Data role, no question, you are right. >> Power role is a different question. A switch of power role with PD should >> not lead to a disconnect. Any other method might. So equating them does >> not look like a good idea. >> > > Not really sure I can follow. If a partner does not support PD, there is no > real distinction between data role and power role, or am I missing something ? > > Are you saying that, if a partner does not support PD, user space should > request a data role swap instead, and that this would be acceptable for you ? > > I don't really understand the difference - a data role swap doesn't cause > a disconnect either if the partner supports PD, and it would still result > in a disconnect/reconnect sequence if the partner does not support PD - > but if it works for you, fine with me. > > Badhri, would that work for us ? Yes Geunter that should work as well. Requesting non-pd role swap either through current_power_role or current_data_role is virtually the same. > > Thanks, > Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
On Thu, May 18, 2017 at 11:13:51AM +0200, Oliver Neukum wrote: > Am Mittwoch, den 17.05.2017, 02:36 -0700 schrieb Guenter Roeck: > > On 05/17/2017 12:34 AM, Oliver Neukum wrote: > > > > > > Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan > > > Sridharan: > > > > > > Hi, > > > > > > > > > > > "Two independent set of mechanisms are defined to allow a USB Type-C > > > > DRP to functionally swap power and data roles. When USB PD is > > > > supported, power and data role swapping is performed as a subsequent > > > > step following the initial connection process. For non-PD > > > > implementations, > > > > power/data role swapping can optionally be dealt with as part of the > > > > initial > > > > connection process." > > > > > > Well, as I read it, without PD once a connection is established, you > > > are stuck with your role. So it seems to me that blocking a later > > > attempt to change it makes sense. > > > > > > > That seems to be a harsh and not very user friendly reading of the > > specification. > > > > I would argue that the user doesn't care if the partner supports PD or not > > when selecting a role, and I would prefer to provide an implementation > > which is > > as user friendly as possible. > > Data role, no question, you are right. > Power role is a different question. A switch of power role with PD should > not lead to a disconnect. Any other method might. So equating them does > not look like a good idea. > Not really sure I can follow. If a partner does not support PD, there is no real distinction between data role and power role, or am I missing something ? Are you saying that, if a partner does not support PD, user space should request a data role swap instead, and that this would be acceptable for you ? I don't really understand the difference - a data role swap doesn't cause a disconnect either if the partner supports PD, and it would still result in a disconnect/reconnect sequence if the partner does not support PD - but if it works for you, fine with me. Badhri, would that work for us ? Thanks, Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
Am Mittwoch, den 17.05.2017, 02:36 -0700 schrieb Guenter Roeck: > On 05/17/2017 12:34 AM, Oliver Neukum wrote: > > > > Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan > > Sridharan: > > > > Hi, > > > > > > > > "Two independent set of mechanisms are defined to allow a USB Type-C > > > DRP to functionally swap power and data roles. When USB PD is > > > supported, power and data role swapping is performed as a subsequent > > > step following the initial connection process. For non-PD implementations, > > > power/data role swapping can optionally be dealt with as part of the > > > initial > > > connection process." > > > > Well, as I read it, without PD once a connection is established, you > > are stuck with your role. So it seems to me that blocking a later > > attempt to change it makes sense. > > > > That seems to be a harsh and not very user friendly reading of the > specification. > > I would argue that the user doesn't care if the partner supports PD or not > when selecting a role, and I would prefer to provide an implementation which > is > as user friendly as possible. Data role, no question, you are right. Power role is a different question. A switch of power role with PD should not lead to a disconnect. Any other method might. So equating them does not look like a good idea. Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
For non-pd case, Should I instead say that the low level driver might optionally choose to perform a best case effort of performing a role swap by disconnect and reconnect ? Does the following description look better ? Description: The supported power roles. This attribute can be used to request power role swap. Swapping is supported as synchronous operation, so write(2) to the attribute will not return until the operation has finished. The attribute is notified about role changes so that poll(2) on the attribute wakes up. Change on the role will also generate uevent KOBJ_CHANGE. The current role is show in brackets, for example "[source] sink" when in source mode. When both the port and the port-partner supports USB Power Delivery, the PR_SWAP command is used to perform the role swap. For non-pd case, the low level driver might optionally perform a best effort approach to swap port roles by forcing a disconnect and reconnect. Thanks, Badhri On Wed, May 17, 2017 at 6:51 AM, Heikki Krogeruswrote: > > On Wed, May 17, 2017 at 06:02:47AM -0700, Guenter Roeck wrote: > > On 05/17/2017 05:38 AM, Heikki Krogerus wrote: > > > Hi guys, > > > > > > On Wed, May 17, 2017 at 02:36:44AM -0700, Guenter Roeck wrote: > > > > On 05/17/2017 12:34 AM, Oliver Neukum wrote: > > > > > Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan > > > > > Sridharan: > > > > > > > > > > Hi, > > > > > > > > > > > "Two independent set of mechanisms are defined to allow a USB Type-C > > > > > > DRP to functionally swap power and data roles. When USB PD is > > > > > > supported, power and data role swapping is performed as a subsequent > > > > > > step following the initial connection process. For non-PD > > > > > > implementations, > > > > > > power/data role swapping can optionally be dealt with as part of > > > > > > the initial > > > > > > connection process." > > > > > > > > > > Well, as I read it, without PD once a connection is established, you > > > > > are stuck with your role. So it seems to me that blocking a later > > > > > attempt to change it makes sense. > > > > > > > > > > > > > That seems to be a harsh and not very user friendly reading of the > > > > specification. > > > > > > > > I would argue that the user doesn't care if the partner supports PD or > > > > not > > > > when selecting a role, and I would prefer to provide an implementation > > > > which is > > > > as user friendly as possible. > > > > > > I agree. But I have to point out that at least with UCSI, the role > > > swapping is usually not possible without USB PD connection. > > > > > > So what I'm trying to say is that we can't really promise that role > > > swapping will ever be possible in all cases without PD, which may mean > > > different behavior depending on the platform. I don't know if that is > > > a huge problem. > > > > > > How predictable do we want this interface to function with role > > > swapping? > > > > > > > We can only do as good as we can, but we should not preclude it either. > > PR_SWAP and other swap operations fail a lot in practice with many dongles, > > just because the PD protocol implementation isn't always stable. So even > > that > > won't be predictable for some time to come. > > > > As Badhri pointed out earlier, at least some low cost devices won't support > > PD. > > Since we are talking about high volume products, we _have_ to make it as > > user friendly as we can, if for nothing else to reduce the number of > > customer > > service calls, repeated bug filings, and, last but not least, to avoid bad > > press. > > OK. So I think we just need to explain in the documentation that there > are no guarantees with role swapping. > > > Thanks, > > -- > heikki -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
On Wed, May 17, 2017 at 06:02:47AM -0700, Guenter Roeck wrote: > On 05/17/2017 05:38 AM, Heikki Krogerus wrote: > > Hi guys, > > > > On Wed, May 17, 2017 at 02:36:44AM -0700, Guenter Roeck wrote: > > > On 05/17/2017 12:34 AM, Oliver Neukum wrote: > > > > Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan > > > > Sridharan: > > > > > > > > Hi, > > > > > > > > > "Two independent set of mechanisms are defined to allow a USB Type-C > > > > > DRP to functionally swap power and data roles. When USB PD is > > > > > supported, power and data role swapping is performed as a subsequent > > > > > step following the initial connection process. For non-PD > > > > > implementations, > > > > > power/data role swapping can optionally be dealt with as part of the > > > > > initial > > > > > connection process." > > > > > > > > Well, as I read it, without PD once a connection is established, you > > > > are stuck with your role. So it seems to me that blocking a later > > > > attempt to change it makes sense. > > > > > > > > > > That seems to be a harsh and not very user friendly reading of the > > > specification. > > > > > > I would argue that the user doesn't care if the partner supports PD or not > > > when selecting a role, and I would prefer to provide an implementation > > > which is > > > as user friendly as possible. > > > > I agree. But I have to point out that at least with UCSI, the role > > swapping is usually not possible without USB PD connection. > > > > So what I'm trying to say is that we can't really promise that role > > swapping will ever be possible in all cases without PD, which may mean > > different behavior depending on the platform. I don't know if that is > > a huge problem. > > > > How predictable do we want this interface to function with role > > swapping? > > > > We can only do as good as we can, but we should not preclude it either. > PR_SWAP and other swap operations fail a lot in practice with many dongles, > just because the PD protocol implementation isn't always stable. So even that > won't be predictable for some time to come. > > As Badhri pointed out earlier, at least some low cost devices won't support > PD. > Since we are talking about high volume products, we _have_ to make it as > user friendly as we can, if for nothing else to reduce the number of customer > service calls, repeated bug filings, and, last but not least, to avoid bad > press. OK. So I think we just need to explain in the documentation that there are no guarantees with role swapping. Thanks, -- heikki -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
On 05/17/2017 05:38 AM, Heikki Krogerus wrote: Hi guys, On Wed, May 17, 2017 at 02:36:44AM -0700, Guenter Roeck wrote: On 05/17/2017 12:34 AM, Oliver Neukum wrote: Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan Sridharan: Hi, "Two independent set of mechanisms are defined to allow a USB Type-C DRP to functionally swap power and data roles. When USB PD is supported, power and data role swapping is performed as a subsequent step following the initial connection process. For non-PD implementations, power/data role swapping can optionally be dealt with as part of the initial connection process." Well, as I read it, without PD once a connection is established, you are stuck with your role. So it seems to me that blocking a later attempt to change it makes sense. That seems to be a harsh and not very user friendly reading of the specification. I would argue that the user doesn't care if the partner supports PD or not when selecting a role, and I would prefer to provide an implementation which is as user friendly as possible. I agree. But I have to point out that at least with UCSI, the role swapping is usually not possible without USB PD connection. So what I'm trying to say is that we can't really promise that role swapping will ever be possible in all cases without PD, which may mean different behavior depending on the platform. I don't know if that is a huge problem. How predictable do we want this interface to function with role swapping? We can only do as good as we can, but we should not preclude it either. PR_SWAP and other swap operations fail a lot in practice with many dongles, just because the PD protocol implementation isn't always stable. So even that won't be predictable for some time to come. As Badhri pointed out earlier, at least some low cost devices won't support PD. Since we are talking about high volume products, we _have_ to make it as user friendly as we can, if for nothing else to reduce the number of customer service calls, repeated bug filings, and, last but not least, to avoid bad press. Thanks, Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
Hi guys, On Wed, May 17, 2017 at 02:36:44AM -0700, Guenter Roeck wrote: > On 05/17/2017 12:34 AM, Oliver Neukum wrote: > > Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan > > Sridharan: > > > > Hi, > > > > > "Two independent set of mechanisms are defined to allow a USB Type-C > > > DRP to functionally swap power and data roles. When USB PD is > > > supported, power and data role swapping is performed as a subsequent > > > step following the initial connection process. For non-PD implementations, > > > power/data role swapping can optionally be dealt with as part of the > > > initial > > > connection process." > > > > Well, as I read it, without PD once a connection is established, you > > are stuck with your role. So it seems to me that blocking a later > > attempt to change it makes sense. > > > > That seems to be a harsh and not very user friendly reading of the > specification. > > I would argue that the user doesn't care if the partner supports PD or not > when selecting a role, and I would prefer to provide an implementation which > is > as user friendly as possible. I agree. But I have to point out that at least with UCSI, the role swapping is usually not possible without USB PD connection. So what I'm trying to say is that we can't really promise that role swapping will ever be possible in all cases without PD, which may mean different behavior depending on the platform. I don't know if that is a huge problem. How predictable do we want this interface to function with role swapping? Thanks, -- heikki -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
On 05/17/2017 01:08 AM, Greg Kroah-Hartman wrote: On Wed, May 17, 2017 at 12:32:19AM -0700, Badhri Jagan Sridharan wrote: With this CL the lower level drivers are reponsible to check and make sure responsible that the role swap can be performed. What is a "CL"? Too much Gerrit. "Change List". Took me a while to understand what people were talking about when talking about CLs. Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
On 05/17/2017 12:34 AM, Oliver Neukum wrote: Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan Sridharan: Hi, "Two independent set of mechanisms are defined to allow a USB Type-C DRP to functionally swap power and data roles. When USB PD is supported, power and data role swapping is performed as a subsequent step following the initial connection process. For non-PD implementations, power/data role swapping can optionally be dealt with as part of the initial connection process." Well, as I read it, without PD once a connection is established, you are stuck with your role. So it seems to me that blocking a later attempt to change it makes sense. That seems to be a harsh and not very user friendly reading of the specification. I would argue that the user doesn't care if the partner supports PD or not when selecting a role, and I would prefer to provide an implementation which is as user friendly as possible. Thanks, Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
On Wed, May 17, 2017 at 12:32:19AM -0700, Badhri Jagan Sridharan wrote: > With this CL the lower level drivers are reponsible to check and make sure > that the role swap can be performed. What is a "CL"? thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers
Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan Sridharan: Hi, > "Two independent set of mechanisms are defined to allow a USB Type-C > DRP to functionally swap power and data roles. When USB PD is > supported, power and data role swapping is performed as a subsequent > step following the initial connection process. For non-PD implementations, > power/data role swapping can optionally be dealt with as part of the initial > connection process." Well, as I read it, without PD once a connection is established, you are stuck with your role. So it seems to me that blocking a later attempt to change it makes sense. Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html