firmware-guide/acpi/gpio-properties.rst

4 _DSD Device Properties Related to GPIO
10 the corresponding GPIO, which is pretty error prone (it depends on
40 The format of the supported GPIO property is::
52   If 1, the GPIO is marked as active_low.
56 it to 1 marks the GPIO as active low.
62 resource, second pin in that resource with the GPIO number of 31.
109           ^GPIO, 19, 0, 0, // chip select 0: GPIO
111           ^GPIO, 20, 0, 0, // chip select 2: GPIO
115 Note, that historically ACPI has no means of the GPIO polarity and thus
117 to avoid a chain of negations, the GPIO polarity is considered being
119 above) the GPIO CS polarity must be defined Active High to avoid ambiguity.
125 _DSD device properties for GPIO controllers:
156 describes each line/pin of a GPIO controller/expander. This list, contained in
157 a package, must be inserted inside the GPIO controller declaration of an ACPI
161   - the first name in the list corresponds with the first line/pin of the GPIO
164   - the list can be incomplete and can end before the last GPIO line: in
165     other words, it is not mandatory to fill all the GPIO lines
168   - names inside one GPIO controller/expander must be unique
170 Example of a GPIO controller of 16 lines, with an incomplete list with two
223 ACPI GPIO Mappings Provided by Drivers
232 to be sufficient to determine the meaning and purpose of all of the GPIO lines
236 to the GPIO lines it is going to use and provide the GPIO subsystem with a
237 mapping between those names and the ACPI GPIO resources corresponding to them.
246 respectively, in analogy with the _DSD GPIO property format specified above.
264 On removal, the driver should unregister its GPIO mapping table by
271 If a device does not have _DSD or the driver does not create ACPI GPIO
272 mapping, the Linux GPIO framework refuses to return any GPIOs. This is
288 The driver might expect to get the right GPIO when it does::
300 The ACPI GPIO mapping tables should not contaminate drivers that are not
302 the ACPI GPIO mapping tables are hardly linked to an ACPI ID and certain
305 Getting GPIO descriptor
308 There are two main approaches to get GPIO resource from ACPI::
327 defined device properties and will prevent to getting any GPIO resources
330 Case 2 explicitly tells GPIO core to look for resources in _CRS.