STMicroelectronics Multi-Function eXpander (STMFX) GPIO expander bindings

ST Multi-Function eXpander (STMFX) offers up to 24 GPIOs expansion.
Please refer to ../mfd/stmfx.txt for STMFX Core bindings.

Required properties:
- compatible: should be "st,stmfx-0300-pinctrl".
- #gpio-cells: should be <2>, the first cell is the GPIO number and the second
  cell is the gpio flags in accordance with <dt-bindings/gpio/gpio.h>.
- gpio-controller: marks the device as a GPIO controller.
- #interrupt-cells: should be <2>, the first cell is the GPIO number and the
  second cell is the interrupt flags in accordance with
  <dt-bindings/interrupt-controller/irq.h>.
- interrupt-controller: marks the device as an interrupt controller.
- gpio-ranges: specifies the mapping between gpio controller and pin
  controller pins. Check "Concerning gpio-ranges property" below.
Please refer to ../gpio/gpio.txt.

Please refer to pinctrl-bindings.txt for pin configuration.

Required properties for pin configuration sub-nodes:
- pins: list of pins to which the configuration applies.

Optional properties for pin configuration sub-nodes (pinconf-generic ones):
- bias-disable: disable any bias on the pin.
- bias-pull-up: the pin will be pulled up.
- bias-pull-pin-default: use the pin-default pull state.
- bias-pull-down: the pin will be pulled down.
- drive-open-drain: the pin will be driven with open drain.
- drive-push-pull: the pin will be driven actively high and low.
- output-high: the pin will be configured as an output driving high level.
- output-low: the pin will be configured as an output driving low level.

Note that STMFX pins[15:0] are called "gpio[15:0]", and STMFX pins[23:16] are
called "agpio[7:0]". Example, to refer to pin 18 of STMFX, use "agpio2".

Concerning gpio-ranges property:
- if all STMFX pins[24:0] are available (no other STMFX function in use), you
  should use gpio-ranges = <&stmfx_pinctrl 0 0 24>;
- if agpio[3:0] are not available (STMFX Touchscreen function in use), you
  should use gpio-ranges = <&stmfx_pinctrl 0 0 16>, <&stmfx_pinctrl 20 20 4>;
- if agpio[7:4] are not available (STMFX IDD function in use), you
  should use gpio-ranges = <&stmfx_pinctrl 0 0 20>;


Example:

	stmfx: stmfx@42 {
		...

		stmfx_pinctrl: stmfx-pin-controller {
			compatible = "st,stmfx-0300-pinctrl";
			#gpio-cells = <2>;
			#interrupt-cells = <2>;
			gpio-controller;
			interrupt-controller;
			gpio-ranges = <&stmfx_pinctrl 0 0 24>;

			joystick_pins: joystick {
				pins = "gpio0", "gpio1", "gpio2", "gpio3", "gpio4";
				drive-push-pull;
				bias-pull-up;
			};
		};
	};

Example of STMFX GPIO consumers:

	joystick {
		compatible = "gpio-keys";
		#address-cells = <1>;
		#size-cells = <0>;
		pinctrl-0 = <&joystick_pins>;
		pinctrl-names = "default";
		button-0 {
			label = "JoySel";
			linux,code = <KEY_ENTER>;
			interrupt-parent = <&stmfx_pinctrl>;
			interrupts = <0 IRQ_TYPE_EDGE_RISING>;
		};
		button-1 {
			label = "JoyDown";
			linux,code = <KEY_DOWN>;
			interrupt-parent = <&stmfx_pinctrl>;
			interrupts = <1 IRQ_TYPE_EDGE_RISING>;
		};
		button-2 {
			label = "JoyLeft";
			linux,code = <KEY_LEFT>;
			interrupt-parent = <&stmfx_pinctrl>;
			interrupts = <2 IRQ_TYPE_EDGE_RISING>;
		};
		button-3 {
			label = "JoyRight";
			linux,code = <KEY_RIGHT>;
			interrupt-parent = <&stmfx_pinctrl>;
			interrupts = <3 IRQ_TYPE_EDGE_RISING>;
		};
		button-4 {
			label = "JoyUp";
			linux,code = <KEY_UP>;
			interrupt-parent = <&stmfx_pinctrl>;
			interrupts = <4 IRQ_TYPE_EDGE_RISING>;
		};
	};

	leds {
		compatible = "gpio-leds";
		orange {
			gpios = <&stmfx_pinctrl 17 1>;
		};

		blue {
			gpios = <&stmfx_pinctrl 19 1>;
		};
	}