Add GPIO hogging documentation to gpio.txt

Signed-off-by: Benoit Parrot <redacted>
---
Changes since v2:
 * Updated to the latest hog syntax.

Changes since v1:
 * Split the devicetree bindings documentation in its own patch.

 Documentation/devicetree/bindings/gpio/gpio.txt | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt
index 3fb8f53..6d88133 100644
--- a/Documentation/devicetree/bindings/gpio/gpio.txt
+++ b/Documentation/devicetree/bindings/gpio/gpio.txt

@@ -103,6 +103,22 @@ Every GPIO controller node must contain both an empty "gpio-controller"
 property, and a #gpio-cells integer property, which indicates the number of
 cells in a gpio-specifier.

+The GPIO chip may contain GPIO hog definitions. GPIO hogging is a mechanism
+providing automatic GPIO request and configuration as part of the
+gpio-controller's driver probe function.
+
+Each GPIO hog definition is represented as a child node of the GPIO controller.
+Required properties:
+- gpio-hog:  A property specifying that this child node represent a gpio-hog.
+- gpios:     Store the gpio information (id, flags, ...). Shall contain the
+            number of cells specified in its parent node (GPIO controller
+            node).