pinctrl: mt8183: add DT binding document

* Mediatek MT8183 Pin Controller

The Mediatek's Pin controller is used to control SoC pins.

Required properties:

- compatible: value should be one of the following.

	"mediatek,mt8183-pinctrl", compatible with mt8183 pinctrl.

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

- #gpio-cells: number of cells in GPIO specifier. Since the generic GPIO

  binding is used, the amount of cells must be specified as 2. See the below

  mentioned gpio binding representation for description of particular cells.

- gpio-ranges : gpio valid number range.

- reg: physical address base for gpio base registers. There are 10 GPIO

  physical address base in mt8183.

Optional properties:

- reg-names: gpio base register names. There are 10 gpio base register

  names in mt8183. They are "iocfg0", "iocfg1", "iocfg2", "iocfg3", "iocfg4",

  "iocfg5", "iocfg6", "iocfg7", "iocfg8", "eint".

- interrupt-controller: Marks the device node as an interrupt controller

- #interrupt-cells: Should be two.

- interrupts : The interrupt outputs to sysirq.

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

common pinctrl bindings used by client devices.

Subnode format

A pinctrl node should contain at least one subnodes representing the

pinctrl groups 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 strength, input enable/disable and input schmitt.

    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

    as macros in boot/dts/<soc>-pinfunc.h directly.

Optional properties:

- GENERIC_PINCONFIG: is the generic pinconfig options to use, bias-disable,

    bias-pull-down, bias-pull-up, input-enable, input-disable, output-low,

    output-high, input-schmitt-enable, input-schmitt-disable

    and drive-strength are valid.

    Some special pins have extra pull up strength, there are R0 and R1 pull-up

    resistors available, but for user, it's only need to set R1R0 as 00, 01,

    10 or 11. So It needs config "mediatek,pull-up-adv" or

    "mediatek,pull-down-adv" to support arguments for those special pins.

    Valid arguments are from 0 to 3.

    mediatek,tdsel: An integer describing the steps for output level shifter

      duty cycle when asserted (high pulse width adjustment). Valid arguments

      are from 0 to 15.

    mediatek,rdsel: An integer describing the steps for input level shifter

      duty cycle when asserted (high pulse width adjustment). Valid arguments

      are from 0 to 63.

    When config drive-strength, it can support some arguments, such as

    MTK_DRIVE_4mA, MTK_DRIVE_6mA, etc. See dt-bindings/pinctrl/mt65xx.h.

    It can only support 2/4/6/8/10/12/14/16mA in mt8183.

    For I2C pins, there are existing generic driving setup and the specific

    driving setup. I2C pins can only support 2/4/6/8/10/12/14/16mA driving

    adjustment in generic driving setup. But in specific driving setup,

    they can support 0.125/0.25/0.5/1mA adjustment. If we enable specific

    driving setup for I2C pins, the existing generic driving setup will be

    disabled. For some special features, we need the I2C pins specific

    driving setup. The specific driving setup is controlled by E1E0EN.

    So we need add extra vendor driving preperty instead of

    the generic driving property.

    We can add "mediatek,drive-strength-adv = <XXX>;" to describe the specific

    driving setup property. "XXX" means the value of E1E0EN. EN is 0 or 1.

    It is used to enable or disable the specific driving setup.

    E1E0 is used to describe the detail strength specification of the I2C pin.

    When E1=0/E0=0, the strength is 0.125mA.

    When E1=0/E0=1, the strength is 0.25mA.

    When E1=1/E0=0, the strength is 0.5mA.

    When E1=1/E0=1, the strength is 1mA.

    So the valid arguments of "mediatek,drive-strength-adv" are from 0 to 7.

Examples:

#include "mt8183-pinfunc.h"

...

{

	pio: pinctrl@10005000 {

		compatible = "mediatek,mt8183-pinctrl";

		reg = <0 0x10005000 0 0x1000>,

		      <0 0x11f20000 0 0x1000>,

		      <0 0x11e80000 0 0x1000>,

		      <0 0x11e70000 0 0x1000>,

		      <0 0x11e90000 0 0x1000>,

		      <0 0x11d30000 0 0x1000>,

		      <0 0x11d20000 0 0x1000>,

		      <0 0x11c50000 0 0x1000>,

		      <0 0x11f30000 0 0x1000>,

		      <0 0x1000b000 0 0x1000>;

		reg-names = "iocfg0", "iocfg1", "iocfg2",

			    "iocfg3", "iocfg4", "iocfg5",

			    "iocfg6", "iocfg7", "iocfg8",

			    "eint";

		gpio-controller;

		#gpio-cells = <2>;

		gpio-ranges = <&pio 0 0 192>;

		interrupt-controller;

		interrupts = <GIC_SPI 177 IRQ_TYPE_LEVEL_HIGH>;

		#interrupt-cells = <2>;

		i2c0_pins_a: i2c0 {

			pins1 {

				pinmux = <PINMUX_GPIO48__FUNC_SCL5>,

					 <PINMUX_GPIO49__FUNC_SDA5>;

				mediatek,pull-up-adv = <3>;

				mediatek,drive-strength-adv = <7>;

			};

		};

		i2c1_pins_a: i2c1 {

			pins {

				pinmux = <PINMUX_GPIO50__FUNC_SCL3>,

					 <PINMUX_GPIO51__FUNC_SDA3>;

				mediatek,pull-down-adv = <2>;

				mediatek,drive-strength-adv = <4>;

			};

		};

		...

	};

};