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gpio: Document GPIO hogging mechanism

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Add GPIO hogging documentation to gpio.txt

Signed-off-by: Benoit Parrot <bparrot@ti.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
This commit is contained in:
Benoit Parrot 2015-02-02 11:44:45 -06:00 committed by Linus Walleij
parent f625d46017
commit 6b516a1093
1 changed files with 30 additions and 0 deletions
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30
Documentation/devicetree/bindings/gpio/gpio.txt
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@ -116,6 +116,29 @@ 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).
Only one of the following properties scanned in the order shown below.
This means that when multiple properties are present they will be searched
in the order presented below and the first match is taken as the intended
configuration.
- input: A property specifying to set the GPIO direction as input.
- output-low A property specifying to set the GPIO direction as output with
the value low.
- output-high A property specifying to set the GPIO direction as output with
the value high.
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 {
@ -123,6 +146,13 @@ 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>;
output-low;
line-name = "foo-bar-gpio";
};
};
qe_pio_e: gpio-controller@1460 {