Documentation: gpio: documentation for optional getters functions

Add a mention about the _optional variants of (devm_)gpiod_get*().

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 23 insertions, 1 deletions

diff --git a/Documentation/gpio/consumer.txt b/Documentation/gpio/consumer.txt
index 76546324e968..6ce544191ca6 100644
--- a/Documentation/gpio/consumer.txt
+++ b/Documentation/gpio/consumer.txt
@@ -53,7 +53,20 @@ with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
 if and only if no GPIO has been assigned to the device/function/index triplet,
 other error codes are used for cases where a GPIO has been assigned but an error
 occurred while trying to acquire it. This is useful to discriminate between mere
-errors and an absence of GPIO for optional GPIO parameters.
+errors and an absence of GPIO for optional GPIO parameters. For the common
+pattern where a GPIO is optional, the gpiod_get_optional() and
+gpiod_get_index_optional() functions can be used. These functions return NULL
+instead of -ENOENT if no GPIO has been assigned to the requested function:
+
+
+        struct gpio_desc *gpiod_get_optional(struct device *dev,
+                                             const char *con_id,
+                                             enum gpiod_flags flags)
+
+        struct gpio_desc *gpiod_get_index_optional(struct device *dev,
+                                                   const char *con_id,
+                                                   unsigned int index,
+                                                   enum gpiod_flags flags)
 
 Device-managed variants of these functions are also defined:
 
@@ -65,6 +78,15 @@ Device-managed variants of these functions are also defined:
                                                unsigned int idx,
                                                enum gpiod_flags flags)
 
+        struct gpio_desc *devm_gpiod_get_optional(struct device *dev,
+                                                  const char *con_id,
+                                                  enum gpiod_flags flags)
+
+        struct gpio_desc * devm_gpiod_get_index_optional(struct device *dev,
+                                                        const char *con_id,
+                                                        unsigned int index,
+                                                        enum gpiod_flags flags)
+
 A GPIO descriptor can be disposed of using the gpiod_put() function:
 
         void gpiod_put(struct gpio_desc *desc)