path: root/Documentation
diff options
authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2014-12-08 19:50:17 +0100
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2014-12-08 19:50:17 +0100
commitd3eaf5875e36b37f1386a4e3e7562c5a6c35abd2 (patch)
tree13f5b6c391ad74a072a4f77f74e958a6ac287032 /Documentation
parentLinux 3.18 (diff)
parentleds: leds-gpio: Fix multiple instances registration without 'label' property (diff)
Merge branch 'device-properties'
* device-properties: leds: leds-gpio: Fix multiple instances registration without 'label' property leds: leds-gpio: Fix legacy GPIO number case ACPI / property: Drop size_prop from acpi_dev_get_property_reference() leds: leds-gpio: Convert gpio_blink_set() to use GPIO descriptors ACPI / GPIO: Document ACPI GPIO mappings API net: rfkill: gpio: Add default GPIO driver mappings for ACPI ACPI / GPIO: Driver GPIO mappings for ACPI GPIOs input: gpio_keys_polled: Make use of device property API leds: leds-gpio: Make use of device property API gpio: Support for unified device properties interface Driver core: Unified interface for firmware node properties input: gpio_keys_polled: Add support for GPIO descriptors leds: leds-gpio: Add support for GPIO descriptors gpio: sch: Consolidate core and resume banks gpio / ACPI: Add support for _DSD device properties misc: at25: Make use of device property API ACPI: Allow drivers to match using Device Tree compatible property Driver core: Unified device properties interface for platform firmware ACPI: Add support for device specific properties
Diffstat (limited to 'Documentation')
2 files changed, 114 insertions, 0 deletions
diff --git a/Documentation/acpi/gpio-properties.txt b/Documentation/acpi/gpio-properties.txt
new file mode 100644
index 000000000000..ae36fcf86dc7
--- /dev/null
+++ b/Documentation/acpi/gpio-properties.txt
@@ -0,0 +1,96 @@
+_DSD Device Properties Related to GPIO
+With the release of ACPI 5.1 and the _DSD configuration objecte names
+can finally be given to GPIOs (and other things as well) returned by
+_CRS. Previously, we were only able to use an integer index to find
+the corresponding GPIO, which is pretty error prone (it depends on
+the _CRS output ordering, for example).
+With _DSD we can now query GPIOs using a name instead of an integer
+index, like the ASL example below shows:
+ // Bluetooth device with reset and shutdown GPIOs
+ Device (BTH)
+ {
+ Name (_HID, ...)
+ Name (_CRS, ResourceTemplate ()
+ {
+ GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
+ "\\_SB.GPO0", 0, ResourceConsumer) {15}
+ GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
+ "\\_SB.GPO0", 0, ResourceConsumer) {27, 31}
+ })
+ Name (_DSD, Package ()
+ {
+ ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+ Package ()
+ {
+ Package () {"reset-gpio", Package() {^BTH, 1, 1, 0 }},
+ Package () {"shutdown-gpio", Package() {^BTH, 0, 0, 0 }},
+ }
+ })
+ }
+The format of the supported GPIO property is:
+ Package () { "name", Package () { ref, index, pin, active_low }}
+ ref - The device that has _CRS containing GpioIo()/GpioInt() resources,
+ typically this is the device itself (BTH in our case).
+ index - Index of the GpioIo()/GpioInt() resource in _CRS starting from zero.
+ pin - Pin in the GpioIo()/GpioInt() resource. Typically this is zero.
+ active_low - If 1 the GPIO is marked as active_low.
+Since ACPI GpioIo() resource does not have a field saying whether it is
+active low or high, the "active_low" argument can be used here. Setting
+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
+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.
diff --git a/Documentation/gpio/consumer.txt b/Documentation/gpio/consumer.txt
index 6ce544191ca6..859918db36b8 100644
--- a/Documentation/gpio/consumer.txt
+++ b/Documentation/gpio/consumer.txt
@@ -219,6 +219,24 @@ part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
+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