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Commit 56b858df authored by Mika Westerberg's avatar Mika Westerberg Committed by Rafael J. Wysocki
Browse files

ACPI: Update GPIO documentation to mention _DSD 



Make sure that the ACPI enumeration.txt provides latest information on how
to describe and retrieve GPIOs now that we can take advantage of _DSD
device properties.

Signed-off-by: default avatarMika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 06e5801b

Documentation/acpi/enumeration.txt

+23 −3
Original line number Diff line number Diff line
@@ -254,8 +254,13 @@ GPIO support 
~~~~~~~~~~~~

ACPI 5 introduced two new resources to describe GPIO connections: GpioIo

and GpioInt. These resources are used be used to pass GPIO numbers used by

the device to the driver. For example:

the device to the driver. ACPI 5.1 extended this with _DSD (Device

Specific Data) which made it possible to name the GPIOs among other things.



For example:



Device (DEV)

{

	Method (_CRS, 0, NotSerialized)

	{

		Name (SBUF, ResourceTemplate()
@@ -285,6 +290,18 @@ the device to the driver. For example: 
		Return (SBUF)

	}



	// ACPI 5.1 _DSD used for naming the GPIOs

	Name (_DSD, Package ()

	{

		ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),

		Package ()

		{

			Package () {"power-gpios", Package() {^DEV, 0, 0, 0 }},

			Package () {"irq-gpios", Package() {^DEV, 1, 0, 0 }},

		}

	})

	...



These GPIO numbers are controller relative and path "\\_SB.PCI0.GPI0"

specifies the path to the controller. In order to use these GPIOs in Linux

we need to translate them to the corresponding Linux GPIO descriptors.
@@ -300,11 +317,11 @@ a code like this: 


	struct gpio_desc *irq_desc, *power_desc;



	irq_desc = gpiod_get_index(dev, NULL, 1);

	irq_desc = gpiod_get(dev, "irq");

	if (IS_ERR(irq_desc))

		/* handle error */



	power_desc = gpiod_get_index(dev, NULL, 0);

	power_desc = gpiod_get(dev, "power");

	if (IS_ERR(power_desc))

		/* handle error */
@@ -313,6 +330,9 @@ a code like this: 
There are also devm_* versions of these functions which release the

descriptors once the device is released.



See Documentation/acpi/gpio-properties.txt for more information about the

_DSD binding related to GPIOs.



MFD devices

~~~~~~~~~~~

The MFD devices register their children as platform devices. For the child