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-rw-r--r--Documentation/devicetree/bindings/gpio/gpio.txt17
1 files changed, 15 insertions, 2 deletions
diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt
index 5788d5cf1252..63b1b9039ce8 100644
--- a/Documentation/devicetree/bindings/gpio/gpio.txt
+++ b/Documentation/devicetree/bindings/gpio/gpio.txt
@@ -52,9 +52,13 @@ only uses one.
gpio-specifier may encode: bank, pin position inside the bank,
whether pin is open-drain and whether pin is logically inverted.
+
Exact meaning of each specifier cell is controller specific, and must
-be documented in the device tree binding for the device. Use the macros
-defined in include/dt-bindings/gpio/gpio.h whenever possible:
+be documented in the device tree binding for the device.
+
+Most controllers are however specifying a generic flag bitfield
+in the last cell, so for these, use the macros defined in
+include/dt-bindings/gpio/gpio.h whenever possible:
Example of a node using GPIOs:
@@ -65,6 +69,15 @@ Example of a node using GPIOs:
GPIO_ACTIVE_HIGH is 0, so in this example gpio-specifier is "18 0" and encodes
GPIO pin number, and GPIO flags as accepted by the "qe_pio_e" gpio-controller.
+Optional standard bitfield specifiers for the last cell:
+
+- Bit 0: 0 means active high, 1 means active low
+- Bit 1: 1 means single-ended wiring, see:
+ https://en.wikipedia.org/wiki/Single-ended_triode
+ When used with active-low, this means open drain/collector, see:
+ https://en.wikipedia.org/wiki/Open_collector
+ When used with active-high, this means open source/emitter
+
1.1) GPIO specifier best practices
----------------------------------

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