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    SubjectRe: [PATCH 04/13] ACPI: Document ACPI device specific properties
    Date
    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.



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