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

[Andy Shevchenko]

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

> 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