pinctrl: dt-binding: document Conexant CX92755 SoC

Conexant Digicolor CX92755 General Purpose Pin Mapping

This document describes the device tree binding of the pin mapping hardware

modules in the Conexant Digicolor CX92755 SoCs. The CX92755 in one of the

Digicolor series of SoCs.

=== Pin Controller Node ===

Required Properties:

- compatible: Must be "cnxt,cx92755-pinctrl"

- reg: Base address of the General Purpose Pin Mapping register block and the

  size of the block.

- gpio-controller: Marks the device node as a GPIO controller.

- #gpio-cells: Must be <2>. The first cell is the pin number and the

  second cell is used to specify flags. See include/dt-bindings/gpio/gpio.h

  for possible values.

For example, the following is the bare minimum node:

	pinctrl: pinctrl@f0000e20 {

		compatible = "cnxt,cx92755-pinctrl";

		reg = <0xf0000e20 0x100>;

		gpio-controller;

		#gpio-cells = <2>;

	};

As a pin controller device, in addition to the required properties, this node

should also contain the pin configuration nodes that client devices reference,

if any.

For a general description of GPIO bindings, please refer to ../gpio/gpio.txt.

=== Pin Configuration Node ===

Each pin configuration node is a sub-node of the pin controller node and is a

container of an arbitrary number of subnodes, called pin group nodes in this

document.

Please refer to the pinctrl-bindings.txt in this directory for details of the

common pinctrl bindings used by client devices, including the definition of a

"pin configuration node".

=== Pin Group Node ===

A pin group node specifies the desired pin mux for an arbitrary number of

pins. The name of the pin group node is optional and not used.

A pin group node only affects the properties specified in the node, and has no

effect on any properties that are omitted.

The pin group node accepts a subset of the generic pin config properties. For

details generic pin config properties, please refer to pinctrl-bindings.txt

and <include/linux/pinctrl/pinconfig-generic.h>.

Required Pin Group Node Properties:

- pins: Multiple strings. Specifies the name(s) of one or more pins to be

  configured by this node. The format of a pin name string is "GP_xy", where x

  is an uppercase character from 'A' to 'R', and y is a digit from 0 to 7.

- function: String. Specifies the pin mux selection. Values must be one of:

  "gpio", "client_a", "client_b", "client_c"

Example:

	pinctrl: pinctrl@f0000e20 {

		compatible = "cnxt,cx92755-pinctrl";

		reg = <0xf0000e20 0x100>;

		uart0_default: uart0_active {

			data_signals {

				pins = "GP_O0", "GP_O1";

				function = "client_b";

			};

		};

	};

	uart0: uart@f0000740 {

		compatible = "cnxt,cx92755-usart";

		...

		pinctrl-0 = <&uart0_default>;

		pinctrl-names = "default";

	};

In the example above, a single pin group configuration node defines the

"client select" for the Rx and Tx signals of uart0. The uart0 node references

that pin configuration node using the &uart0_default phandle.