diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/devicetree/bindings/gpio/gpio.txt | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt index 63b1b9039ce8..e9c49dc4e895 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-1, 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. |