Boards might use the same GPIO line to control several external devices.
Add section to document on how a shared GPIO pin can be described.
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@xxxxxx>
---
.../devicetree/bindings/gpio/gpio.txt | 66 +++++++++++++++++++
1 file changed, 66 insertions(+)
diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt
index a8895d339bfe..644e6513607c 100644
--- a/Documentation/devicetree/bindings/gpio/gpio.txt
+++ b/Documentation/devicetree/bindings/gpio/gpio.txt
@@ -228,6 +228,72 @@ Example of two SOC GPIO banks defined as gpio-controller nodes:
#gpio-cells = <2>;
};
+On boards one GPIO line might be connected to multiple devices as reset, enable
+or other control pins. In order to make it safer for this usage of a GPIO line
+one can describe the shared GPIO pin.
+
+Each shared GPIO pin definition is represented as a child node of the GPIO
+controller.
+
+Required properties:
+- gpio-shared: A property specifying that this child node represents a shared
+ GPIO pin.
+- gpios: Store the GPIO information (id, flags, ...) for each GPIO to
+ affect. Shall contain an integer multiple of 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.
+- output-low: A property specifying to set the GPIO direction as output with
+ the value low initially.
+- output-high: A property specifying to set the GPIO direction as output with
+ the value high initially.
+The shared GPIO line management strategy can be selected with either of the
+following properties:
+- refcounted-low: The line must be kept low as long as there is at least one
+ request asking it to be low.
+- refcounted-high: The line must be kept high as long as there is at least one
+ request asking it to be high.
+If neither of the refcounting strategy was selected then the shared GPIO is
+handled as pass through. In this mode all user requests will be forwarded to the
+shared GPIO pin without refcounting.
+
+Optional properties:
+- line-name: The GPIO label name. If not present the node name is used.
+
+Example of shared GPIO use:
+
+ qe_pio_a: gpio-controller@1400 {
+ compatible = "fsl,qe-pario-bank-a", "fsl,qe-pario-bank";
+ reg = <0x1400 0x18>;
+ gpio-controller;
+ #gpio-cells = <2>;
+
+ line_a {
+ gpio-shared;
+ gpios = <5 0>;
+ output-low;
+ refcounted-high;
+ line-name = "enable-for-devices";
+ };
+ };
+
+ device@0 {
+ compatible = "some,device";
+ enable-gpios = <&qe_pio_a 5 0>;
+ };
+
+ device@1 {
+ compatible = "some,device";
+ enable-gpios = <&qe_pio_a 5 0>;
+ };
+
+ component@0 {
+ compatible = "some,component";
+ select-gpios = <&qe_pio_a 5 0>;
+ };
+
2.1) gpio- and pin-controller interaction
-----------------------------------------
--
Peter
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
