diff options
Diffstat (limited to 'Documentation/devicetree/bindings/gpio/gpio.txt')
| -rw-r--r-- | Documentation/devicetree/bindings/gpio/gpio.txt | 45 |
1 files changed, 42 insertions, 3 deletions
diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt index 5788d5cf1252..069cdf6f9dac 100644 --- a/Documentation/devicetree/bindings/gpio/gpio.txt +++ b/Documentation/devicetree/bindings/gpio/gpio.txt @@ -16,7 +16,9 @@ properties, each containing a 'gpio-list': GPIO properties should be named "[<name>-]gpios", with <name> being the purpose of this GPIO for the device. While a non-existent <name> is considered valid for compatibility reasons (resolving to the "gpios" property), it is not allowed -for new bindings. +for new bindings. Also, GPIO properties named "[<name>-]gpio" are valid and old +bindings use it, but are only supported for compatibility reasons and should not +be used for newer bindings since it has been deprecated. GPIO properties can contain one or more GPIO phandles, but only in exceptional cases should they contain more than one. If your device uses several GPIOs with @@ -52,9 +54,13 @@ 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 +71,15 @@ 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 ---------------------------------- @@ -116,6 +131,30 @@ 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. |