Re: [PATCH 04/13] ACPI: Document ACPI device specific properties

Grant Likely
2014-10-13T12:41:32Z

On Tue, 07 Oct 2014 02:14:06 +0200
, "Rafael J. Wysocki" <rjw@rjwysocki.net>
wrote:
> From: Mika Westerberg <mika.westerberg@linux.intel.com>
>
> This document describes the data format and interfaces of ACPI device
> specific properties.
>
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> Signed-off-by: Darren Hart <dvhart@linux.intel.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> Documentation/acpi/properties.txt | 376 ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 376 insertions(+)
> create mode 100644 Documentation/acpi/properties.txt
>
> Index: linux-pm/Documentation/acpi/properties.txt
> ===================================================================
> --- /dev/null
> +++ linux-pm/Documentation/acpi/properties.txt
> @@ -0,0 +1,376 @@
> +ACPI device properties
> +======================
> +This document describes the format and interfaces of ACPI device
> +properties as specified in "Device Properties UUID For _DSD" available
> +here:
> +
> +http://www.uefi.org/sites/default/files/resources/_DSD-device-properties-UUID.pdf
> +
> +1. Introduction
> +---------------
> +In systems that use ACPI and want to take advantage of device specific
> +properties, there needs to be a standard way to return and extract
> +name-value pairs for a given ACPI device.
> +
> +An ACPI device that wants to export its properties must implement a
> +static name called _DSD that takes no arguments and returns a package of
> +packages:
> +
> + Name (_DSD, Package () {
> + ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> + Package () {
> + Package () {"name1", <VALUE1>},
> + Package () {"name2", <VALUE2>}
> + }
> + })
> +
> +The UUID identifies contents of the following package. In case of ACPI
> +device properties it is daffd814-6eba-4d8c-8a91-bc9bbf4aa301.
> +
> +In each returned package, the first item is the name and must be a string.
> +The corresponding value can be a string, integer, reference, or package. If
> +a package it may only contain strings, integers, and references.
> +
> +An example device where we might need properties is a device that uses
> +GPIOs. In addition to the GpioIo/GpioInt resources the driver needs to
> +know which GPIO is used for which purpose.
> +
> +To solve this we add the following ACPI device properties to the device:
> +
> + Device (DEV0)
> + {
> + Name (_CRS, ResourceTemplate () {
> + GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
> + "\\_SB.PCI0.LPC", 0, ResourceConsumer) {0}
> + GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
> + "\\_SB.PCI0.LPC", 0, ResourceConsumer) {1}
> + ...
> + })
> +
> + Name (_DSD, Package () {
> + ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> + Package () {
> + Package () {"reset-gpio", {^DEV0, 0, 0, 0}},
> + Package () {"shutdown-gpio", {^DEV0, 1, 0, 0}},
> + }
> + })
> + }
> +
> +Now the device driver can reference the GPIOs using names instead of
> +using indexes.

Ummm... so this is kind of odd. Why would arguments be needed for the
gpio reference, or a device trying to reference itself (^DEV0) within
it's own device.

It looks like it is trying to shoehorn DT design patterns into the ACPI
tables when ACPI already has a native method for doing the same thing.
That concerns me.

[...]
> +In addition to simple object references it is also possible to have object
> +references with arguments. These are represented in ASL as follows:
> +
> + Device (\_SB.PCI0.PWM)
> + {
> + Name (_DSD, Package () {
> + ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> + Package () {
> + Package () {"#pwm-cells", 2}
> + }
> + })
> + }
> +
> + Device (\_SB.PCI0.BL)
> + {
> + Name (_DSD, Package () {
> + ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> + Package () {
> + Package () {
> + "pwms",
> + Package () {
> + \_SB.PCI0.PWM, 0, 5000000,
> + \_SB.PCI0.PWM, 1, 4500000,
> + }
> + }
> + }
> + })
> + }

This worries me even more. #x-cells is a very devicetree oriented
pattern that looks wrong for ACPI data. I would expect PWM resources in
ACPI to look much like ACPI GPIO resources or Serial bus resources.

g.