[trimmed my old email] On Wed, Aug 07, 2013 at 10:37:17AM +0300, Pantelis Antoniou wrote: > Hi Greg, > > On Aug 7, 2013, at 8:56 AM, Greg Kroah-Hartman wrote: > > > On Tue, Aug 06, 2013 at 01:27:35PM +0300, Pantelis Antoniou wrote: > >> Hi Greg, > >> > >> On Aug 6, 2013, at 1:15 PM, Greg Kroah-Hartman wrote: > >> > >>> On Tue, Aug 06, 2013 at 12:45:42PM +0300, Pantelis Antoniou wrote: > >>>> Hi Greg, > >>>> > >>>> On Aug 6, 2013, at 12:36 PM, Greg Kroah-Hartman wrote: > >>>> > >>>>> On Tue, Aug 06, 2013 at 10:53:40AM +0300, Pantelis Antoniou wrote: > >>>>>> Platform device removal uncovered a number of problems with > >>>>>> the way resources are handled in the core platform code. > >>>>>> > >>>>>> Resources now form child/parent linkages and this requires > >>>>>> proper linking of the resources. On top of that the OF core > >>>>>> directly creates it's own platform devices. Simplify things > >>>>>> by providing helper functions that manage the linking properly. > >>>>> > >>>>> Ugh, the OF core shouldn't be creating platform devices. Well, yes, I > >>>>> know it does that today, but ick, ick, ick. > >>>>> > >>>> > >>>> Yep, ick, ick, ick is the correct form. > >>>> > >>>>>> Two functions are provided: > >>>>>> > >>>>>> platform_device_link_resources(), which links all the > >>>>>> linkable resources (if not already linked). > >>>>>> > >>>>>> and platform_device_unlink_resources(), which unlinks all the > >>>>>> resources. > >>>>> > >>>>> Why would anyone need to call this? I'm getting the feeling that OF > >>>>> should just have it's own bus of devices to handle this type of mess. > >>>>> ACPI is going through the same rewrite for this same type of problem > >>>>> (they did things differently.) I suggest you work with the ACPI > >>>>> developers to so the same thing they are, to solve it correctly for > >>>>> everyone. > >>>>> > >>>> > >>>> It's the same problem really. Another bus type might not fly well. > >>>> The same device driver should be (in theory) be made to work unchanged > >>>> either on an OF/ACPI/Fex( :) ) setup. > >>> > >>> No, that's not quite true, a driver needs to know how to talk to the > >>> bus, as that is how it communicates to the hardware. It can be done for > >>> different types of busses (see the OHCI USB controller for one example > >>> of this), but a driver will have to know what type of bus it is on in > >>> order to work properly. > >>> > >> > >> In the case of OF & ACPI there is no 'bus'. The device is probably > >> integrated > >> in the SoC's silicon, but there is absolutely no way to 'probe' for it's > >> existence; > >> you have to use a-priori knowledge of the SoC's topology in order to > >> configure it > >> (along with any per-board specific information if there is any kind of > >> shared > >> resource configuration - i.e. pinmuxing or something else). > > > > Not all busses need to have the aiblity to "probe" for new devices, > > that's not a requirement at all. Some of them just "know" where the > > devices are at in the driver model, and create the devices for the bus > > just fine. > > > > So don't think that just because of that lack of probing, they should be > > on the "platform" bus at all. Platform is for the "oh crap, I have no > > way to bind this to anything else, make it a platform device then." > > > > I'm not sure if you remember, but a long time ago when OF started getting > into the kernel, there actually was an OCP (On Chip Peripheral) bus, > and the switch to platform devices was mandated by kernel people, by their > insistance that platform devices would cover every case. > > See here: > > http://lkml.indiana.edu/hypermail/linux/kernel/0405.1/0930.html > > I'm sure Matt Porter can shed some light on the exchange that led to the > abandonment of the ocp bus concept.
Heh, that OCP support looks a bit antiquated by today's standards. If it helps, http://lkml.indiana.edu/hypermail/linux/kernel/0501.2/0696.html is the posting where Kumar starts taking arch/ppc away from using drivers/ocp/. I can't find any public discussion that led to this, but I recall the common advice was "just use platform devices". This was, incidentally, just before the move to arch/powerpc (and DT for all) began. Keep in mind that this is 8ish years ago before embedded was fashionable since we didn't all have Linux machines in our pockets. I suspect that advice was given because nobody cared about platform_device removal and it worked for the use cases at the time. -Matt -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
