dt-bindings: hwmon: Add adt7475 fan/pwm properties

Add fan child nodes that allow describing the connections for the
ADT7475 to the fans it controls. This also allows setting some
initial values for the pwm duty cycle and frequency.
Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20240722221737.3407958-2-chris.packham@alliedtelesis.co.nzSigned-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/devicetree/bindings/hwmon/adt7475.yaml

@@ -51,6 +51,24 @@ properties:
       enum: [0, 1]
       default: 1
 
+  "#pwm-cells":
+    const: 4
+    description: |
+      Number of cells in a PWM specifier.
+      - 0: The PWM channel
+      - 1: The PWM period in nanoseconds
+           - 90909091 (11 Hz)
+           - 71428571 (14 Hz)
+           - 45454545 (22 Hz)
+           - 34482759 (29 Hz)
+           - 28571429 (35 Hz)
+           - 22727273 (44 Hz)
+           - 17241379 (58 Hz)
+           - 11363636 (88 Hz)
+           - 44444 (22 kHz)
+      - 2: PWM flags 0 or PWM_POLARITY_INVERTED
+      - 3: The default PWM duty cycle in nanoseconds
+
 patternProperties:
   "^adi,bypass-attenuator-in[0-4]$":
     description: |
@@ -81,6 +99,10 @@ patternProperties:
       - smbalert#
       - gpio
 
+  "^fan-[0-9]+$":
+    $ref: fan-common.yaml#
+    unevaluatedProperties: false
+
 required:
   - compatible
   - reg
@@ -89,11 +111,12 @@ additionalProperties: false
 
 examples:
   - |
+    #include <dt-bindings/pwm/pwm.h>
     i2c {
       #address-cells = <1>;
       #size-cells = <0>;
 
-      hwmon@2e {
+      pwm: hwmon@2e {
         compatible = "adi,adt7476";
         reg = <0x2e>;
         adi,bypass-attenuator-in0 = <1>;
@@ -101,5 +124,15 @@ examples:
         adi,pwm-active-state = <1 0 1>;
         adi,pin10-function = "smbalert#";
         adi,pin14-function = "tach4";
+        #pwm-cells = <4>;
+
+        /* PWMs at 22.5 kHz frequency, 50% duty*/
+        fan-0 {
+          pwms = <&pwm 0 44444 0 22222>;
+        };
+
+        fan-1 {
+          pwms = <&pwm 2 44444 0 22222>;
+        };
       };
     };