[PATCH v3 13/29] dts: Add a binding for hid-over-i2c

Andy Shevchenko
2020-04-08T20:49:35Z

On Wed, Apr 8, 2020 at 11:40 PM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:
> On Wed, Apr 8, 2020 at 10:39 PM Wolfgang Wallner
> <wolfgang.wallner@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.wallner@br-automation.com> wrote:
> > > > > >An: u-boot at lists.denx.de
> > > > > >Von: "Simon Glass" <sjg@chromium.org>
> > > > > >Datum: 31.03.2020 01:14
> > > > > >Kopie: "Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
> > > > > >"Wolfgang Wallner" <wolfgang.wallner@br-automation.com>, "Leif
> > > > > >Lindholm" <leif@nuviainc.com>, "Simon Glass" <sjg@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.

> > 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
>
> --
> With Best Regards,
> Andy Shevchenko

--
With Best Regards,
Andy Shevchenko