On Wed, Apr 15, 2020 at 04:57:33PM +0200, Wolfgang Wallner wrote: > > On Wed, Apr 15, 2020 at 5:00 PM Wolfgang Wallner > > <wolfgang.wall...@br-automation.com> wrote: > > > -----"Andy Shevchenko" <andy.shevche...@gmail.com> schrieb: ----- > > > > Betreff: Re: Re: [PATCH v3 13/29] dts: Add a binding for hid-over-i2c > > > > > > > > On Wed, Apr 8, 2020 at 11:40 PM Andy Shevchenko > > > > <andy.shevche...@gmail.com> wrote: > > > > > On Wed, Apr 8, 2020 at 10:39 PM Wolfgang Wallner > > > > > <wolfgang.wall...@br-automation.com> wrote: > > > > > > > On Tue, Apr 07, 2020 at 08:58:13PM -0600, Simon Glass wrote: > > > > > > > > On Tue, 31 Mar 2020 at 13:25, Wolfgang Wallner > > > > > > > > <wolfgang.wall...@br-automation.com> wrote: > > > > > > > > > >An: u-boot@lists.denx.de > > > > > > > > > >Von: "Simon Glass" <s...@chromium.org> > > > > > > > > > >Datum: 31.03.2020 01:14 > > > > > > > > > >Kopie: "Andy Shevchenko" <andriy.shevche...@linux.intel.com>, > > > > > > > > > >"Wolfgang Wallner" <wolfgang.wall...@br-automation.com>, > > > > > > > > > >"Leif > > > > > > > > > >Lindholm" <l...@nuviainc.com>, "Simon Glass" > > > > > > > > > ><s...@chromium.org> > > > > > > > > > >Betreff: [PATCH v3 14/29] acpi: Add a binding for ACPI > > > > > > > > > >settings in > > > > > > > > > >the device tree > > > > > > > > > > > > > > > > The _DSD-method for "PRP0001"-devices in ACPI allows to use > > > > > > > > > Devicetree > > > > > > > > > properties inside ACPI, especially it allows to re-use > > > > > > > > > Devicetree's > > > > > > > > > "compatible"-property. But this is for a different use case > > > > > > > > > (using Devicetree > > > > > > > > > properties inside ACPI, not add ACPI properties in > > > > > > > > > Devicetree). > > > > > > > > > > > > > > Before we are going further with this here is a BIG CAVEAT. > > > > > > > > > > > > > > PRP0001 MUST NOT be used in production devices. > > > > > > > > > > > > > > This has been derived solely for debugging / pre-production > > > > > > > testing / etc > > > > > > > purposes. The real devices must have an official ACPI _HID. > > > > > > > > > > > > Thanks for pointing this out! I was not aware of this. > > > > > > I have tried to understand how the PRP0001 is meant to be used, but > > > > > > could not > > > > > > find sufficient documentation. The best document I could find is > > > > > > Documentation/firmware-guide/acpi/enumeration.rst in the Linux > > > > > > kernel, and > > > > > > as far as I can tell the constraint that you mention is also not > > > > > > described > > > > > > there. > > > > > > > > > > > > Do you know any other resources regarding PRP0001, e.g. some kind of > > > > > > speficiation? > > > > > > > > > > I guess the best one is to ask somebody from UEFI Forum / ASWG. PRP is > > > > > a PNP ID for UEFI Forum. > > > > > > > > Basically last message in [3] from Rafael mentions his view on > > > > PRP0001. I guess there is still no document, although as I noticed the > > > > PRP prefix become official in a mean time. > > > > > > Thanks for the references. I have read them carefully, especially the > > > thread > > > in [3]. > > > > > > My understanding up to now was based on presentations by David Woodhouse, > > > so it matches with his viewpoint in the thread at [3]. And as far as I can > > > tell Rafael Wysocki agrees with him in this thread. > > > > > > What I could not find in either of the references is that PRP0001 is only > > > for debugging, I only know about this constraint from your mail. Could you > > > point me to any source for this? > > > > From [3], Rafael said: > > "Let alone the fact that PRP0001 is actually quite useful at the > > prototyping stage when it is premature to allocate a new device ID just > > yet. Taking that to the extreme, if someone whittles a board in his or > > her garage and wants to use it to drive their homemade grass watering > > system, having to invent a new device ID and put it into the existing > > driver that otherwise doesn't require any modifications is ... you know > > what I mean." > > > > It implies that the process should have included the allocation of an > > official ACPI ID. > > I understand the quoted paragraph differently. In the paragraphs above Rafael > argues that PRP0001 is useful, as with PRP0001 we can avoid registering > redundant ACPI IDs. In the quoted paragraph he then gives another example > where PRP0001 is also useful: for debugging. > But I don't understand it in a way that PRP0001 would be limited to only > debugging. > > A few posts before in [4] he explains in more detail, and I think it matches > my understanding of the last post, especially the following sentence: > > "It would be a failure if people had to write separate drivers for > ACPI-based and DT-based platforms to handle the same hardware, at least > at the leaf driver level." >
Maybe better to ask him directly? > [4] https://patchwork.kernel.org/comment/15339311/ > > > You always can ask ASWG for the clarification. Maybe I learn something > > new about PRP0001 :-) > > I had no interaction with ASWG before so I'm not sure what the process is, > but I will look it up. > > > > > > > If PRP0001 is only for debugging, then I must also have > > > > > > misunderstood the > > > > > > Linux "device-property" API (define in include/linux/property.h). > > > > > > > > > > Not exactly. > > > > > > > > > > > There are some presentations available on the internet, e.g. [1], > > > > > > that I > > > > > > understand like PRP0001 + "device-property" API provide a way do > > > > > > access data > > > > > > from either Devicetree or ACPI, depending on what kind of platform > > > > > > you are on. > > > > > > > > > > No, these are not hard linked to each other (the relation is that > > > > > PRP0001 is a way to enumerate devices, which don't have dedicated ACPI > > > > > _HID, by using compatible property [1]). The _DSD per se (i.o.w. > > > > > device properties implementation in ACPI) is a different story [2]. > > > > > > > > > > And I put [3] here, interesting to read. However, at that time I was > > > > > quite far from this topic. > > > > > > > > > > [1]: > > > > > https://www.kernel.org/doc/html/latest/firmware-guide/acpi/enumeration.html#device-tree-namespace-link-device-id > > > > > [2]: > > > > > https://uefi.org/sites/default/files/resources/_DSD-implementation-guide-toplevel-1_2-3.htm. > > > > > [3]: https://patchwork.kernel.org/patch/7004241/ > > > > > > > > > > > [1] > > > > > > https://elinux.org/images/2/2d/Device_tree_acpi_compatibility-david_woodhouse-kernel_recipes_2015.pdf > > regards, Wolfgang -- With Best Regards, Andy Shevchenko
