[Patch v3 2/2] gpio: Document GPIO hogging mechanism

[Benoit Parrot <bparrot@xxxxxx>]

Add GPIO hogging documentation to gpio.txt

Signed-off-by: Benoit Parrot <bparrot@xxxxxx>
---
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).
+- direction: A property specifying the direction/value needed. This property
+	     can take the folowing values: input, output-high, output-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 +126,13 @@ Example of two SOC GPIO banks defined as gpio-controller nodes:
 		reg = <0x1400 0x18>;
 		gpio-controller;
 		#gpio-cells = <2>;
+
+		line_b {
+			gpio-hog;
+			gpios = <6 0>;
+			direction = "output-low";
+			line-name = "foo-bar-gpio";
+		};
 	};
 
 	qe_pio_e: gpio-controller@1460 {
-- 
1.8.5.1

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