dt-binding: hwmon: Add NPCM7xx PWM and Fan controller documentation

Added device tree binding documentation for Nuvoton BMC
NPCM7xx Pulse Width Modulation (PWM) and Fan tach controller.
The Nuvoton BMC NPCM7XX supports 8 PWM controller outputs
and 16 Fan tachometer controller inputs.

Signed-off-by: Tomer Maimon <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
[groeck: Fixed whitespace errors noticed by git]
Signed-off-by: Guenter Roeck <[e-mail]>

Documentation/devicetree/bindings/hwmon/npcm750-pwm-fan.txt

···
+Nuvoton NPCM7xx PWM and Fan Tacho controller device
+
+The Nuvoton BMC NPCM7XX supports 8 Pulse-width modulation (PWM)
+controller outputs and 16 Fan tachometer controller inputs.
+
+Required properties for pwm-fan node
+- #address-cells : should be 1.
+- #size-cells	: should be 0.
+- compatible	: "nuvoton,npcm750-pwm-fan" for Poleg NPCM7XX.
+- reg			: specifies physical base address and size of the registers.
+- reg-names	: must contain:
+					* "pwm" for the PWM registers.
+					* "fan" for the Fan registers.
+- clocks		: phandle of reference clocks.
+- clock-names	: must contain
+					* "pwm" for PWM controller operating clock.
+					* "fan" for Fan controller operating clock.
+- interrupts	: contain the Fan interrupts with flags for falling edge.
+- pinctrl-names	: a pinctrl state named "default" must be defined.
+- pinctrl-0	: phandle referencing pin configuration of the PWM and Fan
+					controller ports.
+
+fan subnode format:
+===================
+Under fan subnode can be upto 8 child nodes, each child node representing a fan.
+Each fan subnode must have one PWM channel and atleast one Fan tach channel.
+
+For PWM channel can be configured cooling-levels to create cooling device.
+Cooling device could be bound to a thermal zone for the thermal control.
+
+Required properties for each child node:
+- reg : specify the PWM output channel.
+	integer value in the range 0 through 7, that represent
+	the PWM channel number that used.
+
+- fan-tach-ch : specify the Fan tach input channel.
+		integer value in the range 0 through 15, that represent
+		the fan tach channel number that used.
+
+		At least one Fan tach input channel is required
+
+Optional property for each child node:
+- cooling-levels: PWM duty cycle values in a range from 0 to 255
+                  which correspond to thermal cooling states.
+
+Examples:
+
+pwm_fan:pwm-fan-controller@103000 {
+	#address-cells = <1>;
+	#size-cells = <0>;
+	compatible = "nuvoton,npcm750-pwm-fan";
+	reg = <0x103000 0x2000>,
+		<0x180000 0x8000>;
+	reg-names = "pwm", "fan";
+	clocks = <&clk NPCM7XX_CLK_APB3>,
+		<&clk NPCM7XX_CLK_APB4>;
+	clock-names = "pwm","fan";
+	interrupts = <GIC_SPI 96 IRQ_TYPE_LEVEL_HIGH>,
+			<GIC_SPI 97 IRQ_TYPE_LEVEL_HIGH>,
+			<GIC_SPI 98 IRQ_TYPE_LEVEL_HIGH>,
+			<GIC_SPI 99 IRQ_TYPE_LEVEL_HIGH>,
+			<GIC_SPI 100 IRQ_TYPE_LEVEL_HIGH>,
+			<GIC_SPI 101 IRQ_TYPE_LEVEL_HIGH>,
+			<GIC_SPI 102 IRQ_TYPE_LEVEL_HIGH>,
+			<GIC_SPI 103 IRQ_TYPE_LEVEL_HIGH>;
+	pinctrl-names = "default";
+	pinctrl-0 = <&pwm0_pins &pwm1_pins &pwm2_pins
+			&fanin0_pins &fanin1_pins &fanin2_pins
+			&fanin3_pins &fanin4_pins>;
+	fan@0 {
+		reg = <0x00>;
+		fan-tach-ch = /bits/ 8 <0x00 0x01>;
+		cooling-levels = <127 255>;
+	};
+	fan@1 {
+		reg = <0x01>;
+		fan-tach-ch = /bits/ 8 <0x02 0x03>;
+	};
+	fan@2 {
+		reg = <0x02>;
+		fan-tach-ch = /bits/ 8 <0x04>;
+	};
+
+};