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

[Wolfgang Wallner]

Hi Andy,

-----"Andy Shevchenko" <andriy.shevchenko at linux.intel.com> schrieb: -----
> 
> Betreff: Re: [PATCH v3 13/29] dts: Add a binding for hid-over-i2c
> 
> 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?

If PRP0001 is only for debugging, then I must also have misunderstood the
Linux "device-property" API (define in include/linux/property.h).
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.

regards, Wolfgang

[1] https://elinux.org/images/2/2d/Device_tree_acpi_compatibility-david_woodhouse-kernel_recipes_2015.pdf