[PATCH v3] Documentation: ACPI: explain how to use gpio-line-names

Flavio Suligoi
2020-11-12T12:52:41Z

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

This commit also fixes a trivial spelling mistake.

Signed-off-by: Flavio Suligoi <f.suligoi@asem.it>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---

v2: - fix commit spelling mistakes
- add double back quotes to gpio-line-names
- adjust documentation lines layout
- add comma at the end of Package list names in the first example

v3: - add: Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

.../firmware-guide/acpi/gpio-properties.rst | 58 ++++++++++++++++++-
1 file changed, 56 insertions(+), 2 deletions(-)

diff --git a/Documentation/firmware-guide/acpi/gpio-properties.rst b/Documentation/firmware-guide/acpi/gpio-properties.rst
index bb6d74f23ee0..ae5396a1f092 100644
--- a/Documentation/firmware-guide/acpi/gpio-properties.rst
+++ b/Documentation/firmware-guide/acpi/gpio-properties.rst
@@ -107,7 +107,61 @@ 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",
@@ -191,7 +245,7 @@ The driver might expect to get the right GPIO when it does::
but since there is no way to know the mapping between "reset" and
the GpioIo() in _CRS desc will hold ERR_PTR(-ENOENT).

-The driver author can solve this by passing the mapping explictly
+The driver author can solve this by passing the mapping explicitly
(the recommended way and documented in the above chapter).

The ACPI GPIO mapping tables should not contaminate drivers that are not
--
2.25.1