gpio / ACPI: Add support for _DSD device properties

With release of ACPI 5.1 and _DSD method we can finally name GPIOs (and
other things as well) returned by _CRS. Previously we were only able to
use integer index to find the corresponding GPIO, which is pretty error
prone if the order changes.

With _DSD we can now query GPIOs using name instead of an integer index,
like the below example shows:

  // Bluetooth device with reset and shutdown GPIOs
  Device (BTH)
  {
      Name (_HID, ...)

      Name (_CRS, ResourceTemplate ()
      {
          GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
                  "\\_SB.GPO0", 0, ResourceConsumer) {15}
          GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
                  "\\_SB.GPO0", 0, ResourceConsumer) {27, 31}
      })

      Name (_DSD, Package ()
      {
          ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
          Package ()
	  {
              Package () {"reset-gpio", Package() {^BTH, 1, 1, 0 }},
              Package () {"shutdown-gpio", Package() {^BTH, 0, 0, 0 }},
          }
      })
  }

The format of the supported GPIO property is:

  Package () { "name", Package () { ref, index, pin, active_low }}

  ref - The device that has _CRS containing GpioIo()/GpioInt() resources,
        typically this is the device itself (BTH in our case).
  index - Index of the GpioIo()/GpioInt() resource in _CRS starting from zero.
  pin - Pin in the GpioIo()/GpioInt() resource. Typically this is zero.
  active_low - If 1 the GPIO is marked as active_low.

Since ACPI GpioIo() resource does not have field saying whether it is
active low or high, the "active_low" argument can be used here. Setting
it to 1 marks the GPIO as active low.

In our Bluetooth example the "reset-gpio" refers to the second GpioIo()
resource, second pin in that resource with the GPIO number of 31.

This patch implements necessary support to gpiolib for extracting GPIOs
using _DSD device properties.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Grant Likely <grant.likely@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 52 insertions, 0 deletions

diff --git a/Documentation/acpi/gpio-properties.txt b/Documentation/acpi/gpio-properties.txt
new file mode 100644
index 000000000000..3e45b8b7e4f2
--- /dev/null
+++ b/Documentation/acpi/gpio-properties.txt
@@ -0,0 +1,52 @@
+_DSD Device Properties Related to GPIO
+--------------------------------------
+
+With the release of ACPI 5.1 and the _DSD configuration objecte names
+can finally be given to GPIOs (and other things as well) returned by
+_CRS.  Previously, we were only able to use an integer index to find
+the corresponding GPIO, which is pretty error prone (it depends on
+the _CRS output ordering, for example).
+
+With _DSD we can now query GPIOs using a name instead of an integer
+index, like the ASL example below shows:
+
+  // Bluetooth device with reset and shutdown GPIOs
+  Device (BTH)
+  {
+      Name (_HID, ...)
+
+      Name (_CRS, ResourceTemplate ()
+      {
+          GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
+                  "\\_SB.GPO0", 0, ResourceConsumer) {15}
+          GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
+                  "\\_SB.GPO0", 0, ResourceConsumer) {27, 31}
+      })
+
+      Name (_DSD, Package ()
+      {
+          ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+          Package ()
+	  {
+              Package () {"reset-gpio", Package() {^BTH, 1, 1, 0 }},
+              Package () {"shutdown-gpio", Package() {^BTH, 0, 0, 0 }},
+          }
+      })
+  }
+
+The format of the supported GPIO property is:
+
+  Package () { "name", Package () { ref, index, pin, active_low }}
+
+  ref - The device that has _CRS containing GpioIo()/GpioInt() resources,
+        typically this is the device itself (BTH in our case).
+  index - Index of the GpioIo()/GpioInt() resource in _CRS starting from zero.
+  pin - Pin in the GpioIo()/GpioInt() resource. Typically this is zero.
+  active_low - If 1 the GPIO is marked as active_low.
+
+Since ACPI GpioIo() resource does not have a field saying whether it is
+active low or high, the "active_low" argument can be used here.  Setting
+it to 1 marks the GPIO as active low.
+
+In our Bluetooth example the "reset-gpio" refers to the second GpioIo()
+resource, second pin in that resource with the GPIO number of 31.