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Documentation: ACPI: explain how to use gpio-line-names

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The "gpio-line-names" declaration is not fully
documented, so can be useful to add some important
information and one more example.

Signed-off-by: Flavio Suligoi <f.suligoi@asem.it>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Flavio Suligoi 2020-11-12 14:15:45 +01:00 committed by Rafael J. Wysocki
parent 09162bc32c
commit 4697958b05
1 changed files with 55 additions and 1 deletions
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56
Documentation/firmware-guide/acpi/gpio-properties.rst
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@ -133,7 +133,61 @@ Example::
- gpio-line-names
Example::
The ``gpio-line-names`` declaration is a list of strings ("names"), which
describes each line/pin of a GPIO controller/expander. This list, contained in
a package, must be inserted inside the GPIO controller declaration of an ACPI
table (typically inside the DSDT). The ``gpio-line-names`` list must respect the
following rules (see also the examples):
- the first name in the list corresponds with the first line/pin of the GPIO
controller/expander
- the names inside the list must be consecutive (no "holes" are permitted)
- the list can be incomplete and can end before the last GPIO line: in
other words, it is not mandatory to fill all the GPIO lines
- empty names are allowed (two quotation marks ``""`` correspond to an empty
name)
Example of a GPIO controller of 16 lines, with an incomplete list with two
empty names::
Package () {
"gpio-line-names",
Package () {
"pin_0",
"pin_1",
"",
"",
"pin_3",
"pin_4_push_button",
}
}
At runtime, the above declaration produces the following result (using the
"libgpiod" tools)::
root@debian:~# gpioinfo gpiochip4
gpiochip4 - 16 lines:
line 0: "pin_0" unused input active-high
line 1: "pin_1" unused input active-high
line 2: unnamed unused input active-high
line 3: unnamed unused input active-high
line 4: "pin_3" unused input active-high
line 5: "pin_4_push_button" unused input active-high
line 6: unnamed unused input active-high
line 7 unnamed unused input active-high
line 8: unnamed unused input active-high
line 9: unnamed unused input active-high
line 10: unnamed unused input active-high
line 11: unnamed unused input active-high
line 12: unnamed unused input active-high
line 13: unnamed unused input active-high
line 14: unnamed unused input active-high
line 15: unnamed unused input active-high
root@debian:~# gpiofind pin_4_push_button
gpiochip4 5
root@debian:~#
Another example::
Package () {
"gpio-line-names",