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ACPI: Update GPIO documentation to mention _DSD

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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: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Mika Westerberg 2015-03-17 12:40:12 +02:00 committed by Rafael J. Wysocki
parent 06e5801b8c
commit 56b858dfad
1 changed files with 23 additions and 3 deletions
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26
Documentation/acpi/enumeration.txt
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@ -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