dt-bindings: backlight: Add brightness-levels related common properties

Both files pwm-backlight.yaml and led-backlight.yaml contain properties
in common with each other, regarding the brightness levels:

- brightness-levels
- default-brightness-level

These properties can then be moved to backlight/common.yaml.
Signed-off-by: Flavio Suligoi <f.suligoi@asem.it>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20231016150554.27144-1-f.suligoi@asem.itSigned-off-by: Lee Jones <lee@kernel.org>

Documentation/devicetree/bindings/leds/backlight/common.yaml

@@ -33,4 +33,21 @@ properties:
       due to restrictions in a specific system, such as mounting conditions.
     $ref: /schemas/types.yaml#/definitions/uint32
 
+  brightness-levels:
+    description:
+      Array of distinct brightness levels. The levels must be in the range
+      accepted by the underlying LED device. Typically these are in the range
+      from 0 to 255, but any range starting at 0 will do, as long as they are
+      accepted by the LED.
+      The 0 value means a 0% of brightness (darkest/off), while the last value
+      in the array represents a full 100% brightness (brightest).
+      If this array is not provided, the driver default mapping is used.
+    $ref: /schemas/types.yaml#/definitions/uint32-array
+
+  default-brightness-level:
+    description:
+      The default brightness level (index into the array defined by the
+      "brightness-levels" property).
+    $ref: /schemas/types.yaml#/definitions/uint32
+
 additionalProperties: true

Documentation/devicetree/bindings/leds/backlight/led-backlight.yaml

@@ -16,6 +16,9 @@ description:
   can also be used to describe a backlight device controlled by the output of
   a LED driver.
 
+allOf:
+  - $ref: common.yaml#
+
 properties:
   compatible:
     const: led-backlight
@@ -26,25 +29,11 @@ properties:
     items:
       maxItems: 1
 
-  brightness-levels:
-    description:
-      Array of distinct brightness levels. The levels must be in the range
-      accepted by the underlying LED devices. This is used to translate a
-      backlight brightness level into a LED brightness level. If it is not
-      provided, the identity mapping is used.
-    $ref: /schemas/types.yaml#/definitions/uint32-array
-
-  default-brightness-level:
-    description:
-      The default brightness level (index into the array defined by the
-      "brightness-levels" property).
-    $ref: /schemas/types.yaml#/definitions/uint32
-
 required:
   - compatible
   - leds
 
-additionalProperties: false
+unevaluatedProperties: false
 
 examples:
   - |

Documentation/devicetree/bindings/leds/backlight/pwm-backlight.yaml

@@ -11,6 +11,9 @@ maintainers:
   - Daniel Thompson <daniel.thompson@linaro.org>
   - Jingoo Han <jingoohan1@gmail.com>
 
+allOf:
+  - $ref: common.yaml#
+
 properties:
   compatible:
     const: pwm-backlight
@@ -39,21 +42,6 @@ properties:
       Delay in ms between disabling the backlight using GPIO and setting PWM
       value to 0.
 
-  brightness-levels:
-    description:
-      Array of distinct brightness levels. Typically these are in the range
-      from 0 to 255, but any range starting at 0 will do. The actual brightness
-      level (PWM duty cycle) will be interpolated from these values. 0 means a
-      0% duty cycle (darkest/off), while the last value in the array represents
-      a 100% duty cycle (brightest).
-    $ref: /schemas/types.yaml#/definitions/uint32-array
-
-  default-brightness-level:
-    description:
-      The default brightness level (index into the array defined by the
-      "brightness-levels" property).
-    $ref: /schemas/types.yaml#/definitions/uint32
-
   num-interpolated-steps:
     description:
       Number of interpolated steps between each value of brightness-levels
@@ -69,7 +57,7 @@ required:
   - compatible
   - pwms
 
-additionalProperties: false
+unevaluatedProperties: false
 
 examples:
   - |