pinctrl: Add DT bindings for PIC32 pin control and GPIO

Document the devicetree bindings for PINCTRL and GPIO found on Microchip
PIC32 class devices.
Signed-off-by: Joshua Henderson <joshua.henderson@microchip.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Acked-by: Rob Herring <robh@kernel.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/gpio/microchip,pic32-gpio.txt

+* Microchip PIC32 GPIO devices (PIO).
+
+Required properties:
+ - compatible: "microchip,pic32mzda-gpio"
+ - reg: Base address and length for the device.
+ - interrupts: The port interrupt shared by all pins.
+ - gpio-controller: Marks the port as GPIO controller.
+ - #gpio-cells: Two. The first cell is the pin number and
+   the second cell is used to specify the gpio polarity as defined in
+   defined in <dt-bindings/gpio/gpio.h>:
+      0 = GPIO_ACTIVE_HIGH
+      1 = GPIO_ACTIVE_LOW
+      2 = GPIO_OPEN_DRAIN
+ - interrupt-controller: Marks the device node as an interrupt controller.
+ - #interrupt-cells: Two. The first cell is the GPIO number and second cell
+   is used to specify the trigger type as defined in
+   <dt-bindings/interrupt-controller/irq.h>:
+      IRQ_TYPE_EDGE_RISING
+      IRQ_TYPE_EDGE_FALLING
+      IRQ_TYPE_EDGE_BOTH
+ - clocks: Clock specifier (see clock bindings for details).
+ - microchip,gpio-bank: Specifies which bank a controller owns.
+ - gpio-ranges: Interaction with the PINCTRL subsystem.
+
+Example:
+
+/* PORTA */
+gpio0: gpio0@1f860000 {
+	compatible = "microchip,pic32mzda-gpio";
+	reg = <0x1f860000 0x100>;
+	interrupts = <118 IRQ_TYPE_LEVEL_HIGH>;
+	#gpio-cells = <2>;
+	gpio-controller;
+	interrupt-controller;
+	#interrupt-cells = <2>;
+	clocks = <&PBCLK4>;
+	microchip,gpio-bank = <0>;
+	gpio-ranges = <&pic32_pinctrl 0 0 16>;
+};
+
+keys {
+	...
+
+	button@sw1 {
+		label = "ESC";
+		linux,code = <1>;
+		gpios = <&gpio0 12 0>;
+	};
+};

Documentation/devicetree/bindings/pinctrl/microchip,pic32-pinctrl.txt

+* Microchip PIC32 Pin Controller
+
+Please refer to pinctrl-bindings.txt, ../gpio/gpio.txt, and
+../interrupt-controller/interrupts.txt for generic information regarding
+pin controller, GPIO, and interrupt bindings.
+
+PIC32 'pin configuration node' is a node of a group of pins which can be
+used for a specific device or function. This node represents configuraions of
+pins, optional function, and optional mux related configuration.
+
+Required properties for pin controller node:
+ - compatible: "microchip,pic32mada-pinctrl"
+ - reg: Address range of the pinctrl registers.
+ - clocks: Clock specifier (see clock bindings for details)
+
+Required properties for pin configuration sub-nodes:
+ - pins: List of pins to which the configuration applies.
+
+Optional properties for pin configuration sub-nodes:
+----------------------------------------------------
+ - function: Mux function for the specified pins.
+ - bias-pull-up: Enable weak pull-up.
+ - bias-pull-down: Enable weak pull-down.
+ - input-enable: Set the pin as an input.
+ - output-low: Set the pin as an output level low.
+ - output-high: Set the pin as an output level high.
+ - microchip,digital: Enable digital I/O.
+ - microchip,analog: Enable analog I/O.
+
+Example:
+
+pic32_pinctrl: pinctrl@1f801400{
+	#address-cells = <1>;
+	#size-cells = <1>;
+	compatible = "microchip,pic32mzda-pinctrl";
+	reg = <0x1f801400 0x400>;
+	clocks = <&PBCLK1>;
+
+	pinctrl_uart2: pinctrl_uart2 {
+		uart2-tx {
+			pins = "G9";
+			function = "U2TX";
+			microchip,digital;
+			output-low;
+		};
+		uart2-rx {
+			pins = "B0";
+			function = "U2RX";
+			microchip,digital;
+			input-enable;
+		};
+	};
+};
+
+uart2: serial@1f822200 {
+	compatible = "microchip,pic32mzda-uart";
+	reg = <0x1f822200 0x50>;
+	pinctrl-names = "default";
+	pinctrl-0 = <&pinctrl_uart2>;
+};