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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 <rafael.j.wysocki@intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
This commit is contained in:
Rafael J. Wysocki 2014-11-03 23:39:57 +01:00
parent 72daceb9a1
commit e36d453e98
2 changed files with 62 additions and 0 deletions
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44
Documentation/acpi/gpio-properties.txt
View File

@ -50,3 +50,47 @@ 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.
ACPI GPIO Mappings Provided by Drivers
--------------------------------------
There are systems in which the ACPI tables do not contain _DSD but provide _CRS
with GpioIo()/GpioInt() resources and device drivers still need to work with
them.
In those cases ACPI device identification objects, _HID, _CID, _CLS, _SUB, _HRV,
available to the driver can be used to identify the device and that is supposed
to be sufficient to determine the meaning and purpose of all of the GPIO lines
listed by the GpioIo()/GpioInt() resources returned by _CRS. In other words,
the driver is supposed to know what to use the GpioIo()/GpioInt() resources for
once it has identified the device. Having done that, it can simply assign names
to the GPIO lines it is going to use and provide the GPIO subsystem with a
mapping between those names and the ACPI GPIO resources corresponding to them.
To do that, the driver needs to define a mapping table as a NULL-terminated
array of struct acpi_gpio_mapping objects that each contain a name, a pointer
to an array of line data (struct acpi_gpio_params) objects and the size of that
array. Each struct acpi_gpio_params object consists of three fields,
crs_entry_index, line_index, active_low, representing the index of the target
GpioIo()/GpioInt() resource in _CRS starting from zero, the index of the target
line in that resource starting from zero, and the active-low flag for that line,
respectively, in analogy with the _DSD GPIO property format specified above.
For the example Bluetooth device discussed previously the data structures in
question would look like this:
static const struct acpi_gpio_params reset_gpio = { 1, 1, false };
static const struct acpi_gpio_params shutdown_gpio = { 0, 0, false };
static const struct acpi_gpio_mapping bluetooth_acpi_gpios[] = {
{ "reset-gpio", &reset_gpio, 1 },
{ "shutdown-gpio", &shutdown_gpio, 1 },
{ },
};
Next, the mapping table needs to be passed as the second argument to
acpi_dev_add_driver_gpios() that will register it with the ACPI device object
pointed to by its first argument. That should be done in the driver's .probe()
routine. On removal, the driver should unregister its GPIO mapping table by
calling acpi_dev_remove_driver_gpios() on the ACPI device object where that
table was previously registered.

18
Documentation/gpio/consumer.txt
View File

@ -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