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ACPI / GPIO: Document ACPI GPIO mappings API

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Document the previously introduced method that can be used by device
drivers to provide the GPIO subsystem with mappings between GPIO names
(connection IDs) and GpioIo()/GpioInt() resources in _CRS.

Signed-off-by: Rafael J. Wysocki <[email protected]>
Reviewed-by: Mika Westerberg <[email protected]>
This commit is contained in:
Rafael J. Wysocki 2014-11-03 23:39:57 +01:00
commit e36d453e98
2 changed files with 62 additions and 0 deletions
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18
Documentation/gpio/consumer.txt
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@ -219,6 +219,24 @@ part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
capabilities.
GPIOs and ACPI
==============
On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
the _CRS configuration objects of devices. Those resources do not provide
connection IDs (names) for GPIOs, so it is necessary to use an additional
mechanism for this purpose.
Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
which, among other things, may be used to provide connection IDs for specific
GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the
case, it will be handled by the GPIO subsystem automatically. However, if the
_DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
connection IDs need to be provided by device drivers.
For details refer to Documentation/acpi/gpio-properties.txt
Interacting With the Legacy GPIO Subsystem
==========================================
Many kernel subsystems still handle GPIOs using the legacy integer-based