Documentation: dt-bindings: Document bindings for ASPEED AST2400/AST2500 PWM and...

This binding provides interface for adding values related to ASPEED
AST2400/2500 PWM and Fan tach controller support.
The PWM controller can support upto 8 PWM output ports.
The Fan tach controller can support upto 16 tachometer inputs.

Signed-off-by: Jaghathiswari Rankappagounder Natarajan <jaghu@google.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/Documentation/devicetree/bindings/hwmon/aspeed-pwm-tacho.txt b/Documentation/devicetree/bindings/hwmon/aspeed-pwm-tacho.txt
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+ASPEED AST2400/AST2500 PWM and Fan Tacho controller device driver
+
+The ASPEED PWM controller can support upto 8 PWM outputs. The ASPEED Fan Tacho
+controller can support upto 16 Fan tachometer inputs.
+
+There can be upto 8 fans supported. Each fan can have one PWM output and
+one/two Fan tach inputs.
+
+Required properties for pwm-tacho node:
+- #address-cells : should be 1.
+
+- #size-cells : should be 1.
+
+- reg : address and length of the register set for the device.
+
+- pinctrl-names : a pinctrl state named "default" must be defined.
+
+- pinctrl-0 : phandle referencing pin configuration of the PWM ports.
+
+- compatible : should be "aspeed,ast2400-pwm-tacho" for AST2400 and
+              "aspeed,ast2500-pwm-tacho" for AST2500.
+
+- clocks : a fixed clock providing input clock frequency(PWM
+          and Fan Tach clock)
+
+fan subnode format:
+===================
+Under fan subnode there can upto 8 child nodes, with each child node
+representing a fan. If there are 8 fans each fan can have one PWM port and
+one/two Fan tach inputs.
+
+Required properties for each child node:
+- reg : should specify PWM source port.
+       integer value in the range 0 to 7 with 0 indicating PWM port A and
+       7 indicating PWM port H.
+
+- aspeed,fan-tach-ch : should specify the Fan tach input channel.
+                integer value in the range 0 through 15, with 0 indicating
+               Fan tach channel 0 and 15 indicating Fan tach channel 15.
+               Atleast one Fan tach input channel is required.
+
+Examples:
+
+pwm_tacho_fixed_clk: fixedclk {
+       compatible = "fixed-clock";
+       #clock-cells = <0>;
+       clock-frequency = <24000000>;
+};
+
+pwm_tacho: pwmtachocontroller@1e786000 {
+       #address-cells = <1>;
+       #size-cells = <1>;
+       reg = <0x1E786000 0x1000>;
+       compatible = "aspeed,ast2500-pwm-tacho";
+       clocks = <&pwm_tacho_fixed_clk>;
+       pinctrl-names = "default";
+       pinctrl-0 = <&pinctrl_pwm0_default &pinctrl_pwm1_default>;
+
+       fan@0 {
+               reg = <0x00>;
+               aspeed,fan-tach-ch = /bits/ 8 <0x00>;
+       };
+
+       fan@1 {
+               reg = <0x01>;
+               aspeed,fan-tach-ch = /bits/ 8 <0x01 0x02>;
+       };
+};