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@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.
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#... [2]: https://uefi.org/sites/default/files/resources/_DSD-implementation-guide-top.... [3]: https://patchwork.kernel.org/patch/7004241/
[1] https://elinux.org/images/2/2d/Device_tree_acpi_compatibility-david_woodhous...