[Patch v2 2/2] gpio: Document GPIO hogging mechanism

[Benoit Parrot <bparrot@ti.com>]

Add GPIO hogging documentation to gpio.txt

Signed-off-by: Benoit Parrot <bparrot@ti.com>
---
Changes since v1:
 * Split the devicetree bindings documentation in its own patch.

 Documentation/devicetree/bindings/gpio/gpio.txt | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt
index 3fb8f53..82755e2 100644
--- a/Documentation/devicetree/bindings/gpio/gpio.txt
+++ b/Documentation/devicetree/bindings/gpio/gpio.txt
@@ -103,6 +103,24 @@ 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).
+- input: a property specifying to set the GPIO direction as input.
+- output-high: a property specifying to set the GPIO direction to output with
+  the value high.
+- output-low: a property specifying to set the GPIO direction to output with
+  the value low.
+
+Optional properties:
+- line-name: the GPIO label name. If not present the node name is used.
+
 Example of two SOC GPIO banks defined as gpio-controller nodes:
 
 	qe_pio_a: gpio-controller@1400 {
@@ -110,6 +128,13 @@ Example of two SOC GPIO banks defined as gpio-controller nodes:
 		reg = <0x1400 0x18>;
 		gpio-controller;
 		#gpio-cells = <2>;
+
+		line_b: line_b {
+			gpio-hog;
+			gpios = <6 0>;
+			output-low;
+			line-name = "foo-bar-gpio";
+		};
 	};
 
 	qe_pio_e: gpio-controller@1460 {
-- 
1.8.5.1