[PATCH 2/2 v2] Documentation: gpio: board: describe the con_id parameter

[Dirk Behme <dirk.behme@xxxxxxxxx>]

The con_id parameter has to match the GPIO description and is automatically
extended by the GPIO suffix if not NULL. I had to look into the code to
understand this and properly find the GPIO I've been looking for, so document
this.

Signed-off-by: Dirk Behme <dirk.behme@xxxxxxxxx>
---
Changes in v2: Using the "gpios" property without prefix is considered deprecated,
               therefore don't describe it.

 Documentation/gpio/board.txt    | 9 +++++++++
 Documentation/gpio/consumer.txt | 3 +++
 2 files changed, 12 insertions(+)

diff --git a/Documentation/gpio/board.txt b/Documentation/gpio/board.txt
index 7605773..0bfc455 100644
--- a/Documentation/gpio/board.txt
+++ b/Documentation/gpio/board.txt
@@ -48,6 +48,15 @@ This property will make GPIOs 15, 16 and 17 available to the driver under the
 The led GPIOs will be active-high, while the power GPIO will be active-low (i.e.
 gpiod_is_active_low(power) will be true).
 
+The second parameter of the gpiod_get() functions, the con_id string, has to be
+the <function>-prefix of the GPIO suffixes ("gpios" or "gpio", automatically
+looked up by the gpiod functions internally) used in the device tree. With above
+"led-gpios" example, use the prefix without the "-" as con_id parameter: "led".
+
+Internally, the GPIO subsystem prefixes the GPIO suffix ("gpios" or "gpio")
+with the string passed in con_id to get the resulting string
+(snprintf(... "%s-%s", con_id, gpio_suffixes[]).
+
 ACPI
 ----
 ACPI also supports function names for GPIOs in a similar fashion to DT.
diff --git a/Documentation/gpio/consumer.txt b/Documentation/gpio/consumer.txt
index 75542b9..47ce4fd 100644
--- a/Documentation/gpio/consumer.txt
+++ b/Documentation/gpio/consumer.txt
@@ -39,6 +39,9 @@ device that displays digits), an additional index argument can be specified:
 					  const char *con_id, unsigned int idx,
 					  enum gpiod_flags flags)
 
+For a more detailed description of the con_id parameter in the DeviceTree case
+see Documentation/gpio/board.txt
+
 The flags parameter is used to optionally specify a direction and initial value
 for the GPIO. Values can be:
 
-- 
2.5.1

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