There are a bunch of drivers that utilize the "ngpios" DT property
without any vendor prefix. Try to start cleaning up the mess by
defining what we mean by this property.
Cc: devicetree@vger.kernel.org
Cc: Pramod Kumar <pramo...@broadcom.com>
Cc: Jonas Gorski <j...@openwrt.org>
Signed-off-by: Linus Walleij <linus.wall...@linaro.org>
---
Documentation/devicetree/bindings/gpio/gpio.txt | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt
b/Documentation/devicetree/bindings/gpio/gpio.txt
index 63b1b9039ce8..9b081e6143a0 100644
--- a/Documentation/devicetree/bindings/gpio/gpio.txt
+++ b/Documentation/devicetree/bindings/gpio/gpio.txt
@@ -129,6 +129,30 @@ 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.
+Optionally, a GPIO controller may have a "ngpios" property. This property
+indicates the number of in-use slots of available slots for GPIOs. The
+typical example is something like this: the hardware register is 32 bits
+wide, but only 18 of the bits have a physical counterpart. The driver is
+generally written so that all 32 bits can be used, but the IP block is reused
+in a lot of designs, some using all 32 bits, some using 18 and some using
+12. In this case, setting "ngpios = <18>;" informs the driver that only the
+first 18 GPIOs, at local offset 0 .. 17, are in use.
+
+If these GPIOs do not happen to be the first N GPIOs at offset 0...N, an
+additional bitmask is needed to specify which GPIOs are actually in use,
+and which are dummies. The bindings for this case has not yet been
+specified, but should be specified if/when such hardware appears.
+
+Example:
+
+gpio-controller@00000000 {
+ compatible = "foo";
+ reg = <0x00000000 0x1000>;
+ gpio-controller;
+ #gpio-cells = <2>;
+ ngpios = <18>;
+}
+
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.
--
2.4.3
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