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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 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 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) Method (_CRS, 0, NotSerialized)
{ {
Name (SBUF, ResourceTemplate() Name (SBUF, ResourceTemplate()
@ -285,6 +290,18 @@ the device to the driver. For example:
Return (SBUF) 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" 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 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. 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; 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)) if (IS_ERR(irq_desc))
/* handle error */ /* handle error */
power_desc = gpiod_get_index(dev, NULL, 0); power_desc = gpiod_get(dev, "power");
if (IS_ERR(power_desc)) if (IS_ERR(power_desc))
/* handle error */ /* handle error */
@ -313,6 +330,9 @@ a code like this:
There are also devm_* versions of these functions which release the There are also devm_* versions of these functions which release the
descriptors once the device is released. descriptors once the device is released.
See Documentation/acpi/gpio-properties.txt for more information about the
_DSD binding related to GPIOs.
MFD devices MFD devices
~~~~~~~~~~~ ~~~~~~~~~~~
The MFD devices register their children as platform devices. For the child The MFD devices register their children as platform devices. For the child