Documentation: dt-bindings: Document STM32 pinctrl driver DT bindings

* STM32 GPIO and Pin Mux/Config controller

STMicroelectronics's STM32 MCUs intregrate a GPIO and Pin mux/config hardware

controller. It controls the input/output settings on the available pins and

also provides ability to multiplex and configure the output of various on-chip

controllers onto these pads.

Pin controller node:

Required properies:

 - compatible: value should be one of the following:

   (a) "st,stm32f429-pinctrl"

 - #address-cells: The value of this property must be 1

 - #size-cells	: The value of this property must be 1

 - ranges	: defines mapping between pin controller node (parent) to

   gpio-bank node (children).

 - pins-are-numbered: Specify the subnodes are using numbered pinmux to

   specify pins.

GPIO controller/bank node:

Required properties:

 - gpio-controller : Indicates this device is a GPIO controller

 - #gpio-cells	  : Should be two.

			The first cell is the pin number

			The second one is the polarity:

				- 0 for active high

				- 1 for active low

 - reg		  : The gpio address range, relative to the pinctrl range

 - clocks	  : clock that drives this bank

 - st,bank-name	  : Should be a name string for this bank as specified in

   the datasheet

Optional properties:

 - reset:	  : Reference to the reset controller

Example:

#include <dt-bindings/pinctrl/stm32f429-pinfunc.h>

...

	pin-controller {

		#address-cells = <1>;

		#size-cells = <1>;

		compatible = "st,stm32f429-pinctrl";

		ranges = <0 0x40020000 0x3000>;

		pins-are-numbered;

		gpioa: gpio@40020000 {

			gpio-controller;

			#gpio-cells = <2>;

			reg = <0x0 0x400>;

			resets = <&reset_ahb1 0>;

			st,bank-name = "GPIOA";

		};

		...

		pin-functions nodes follow...

	};

Contents of function subnode node:

----------------------------------

Subnode format

A pinctrl node should contain at least one subnode representing the

pinctrl group available on the machine. Each subnode will list the

pins it needs, and how they should be configured, with regard to muxer

configuration, pullups, drive, output high/low and output speed.

    node {

	pinmux = <PIN_NUMBER_PINMUX>;

	GENERIC_PINCONFIG;

    };

Required properties:

- pinmux: integer array, represents gpio pin number and mux setting.

  Supported pin number and mux varies for different SoCs, and are defined in

  dt-bindings/pinctrl/<soc>-pinfunc.h directly.

  These defines are calculated as:

    ((port * 16 + line) << 8) | function

  With:

    - port: The gpio port index (PA = 0, PB = 1, ..., PK = 11)

    - line: The line offset within the port (PA0 = 0, PA1 = 1, ..., PA15 = 15)

    - function: The function number, can be:

      * 0 : GPIO

      * 1 : Alternate Function 0

      * 2 : Alternate Function 1

      * 3 : Alternate Function 2

      * ...

      * 16 : Alternate Function 15

      * 17 : Analog

Optional properties:

- GENERIC_PINCONFIG: is the generic pinconfig options to use.

  Available options are:

   - bias-disable,

   - bias-pull-down,

   - bias-pull-up,

   - drive-push-pull,

   - drive-open-drain,

   - output-low

   - output-high

   - slew-rate = <x>, with x being:

       < 0 > : Low speed

       < 1 > : Medium speed

       < 2 > : Fast speed

       < 3 > : High speed

Example:

pin-controller {

...

	usart1_pins_a: usart1@0 {

		pins1 {

			pinmux = <STM32F429_PA9_FUNC_USART1_TX>;

			bias-disable;

			drive-push-pull;

			slew-rate = <0>;

		};

		pins2 {

			pinmux = <STM32F429_PA10_FUNC_USART1_RX>;

			bias-disable;

		};

	};

};

&usart1 {

	pinctrl-0 = <&usart1_pins_a>;

	pinctrl-names = "default";

	status = "okay";

};