dt-bindings: backlight: Add MediaTek MT6370 backlight

Add MT6370 backlight binding documentation.
Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Signed-off-by: ChiaEn Wu <chiaen_wu@richtek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20220830034042.9354-5-peterwu.pub@gmail.com

Documentation/devicetree/bindings/leds/backlight/mediatek,mt6370-backlight.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/leds/backlight/mediatek,mt6370-backlight.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MediaTek MT6370 Backlight
+
+maintainers:
+  - ChiaEn Wu <chiaen_wu@richtek.com>
+
+description: |
+  This module is part of the MT6370 MFD device.
+  The MT6370 Backlight WLED driver supports up to a 29V output voltage for
+  4 channels of 8 series WLEDs. Each channel supports up to 30mA of current
+  capability with 2048 current steps (11 bits, only for MT6370/MT6371) or
+  16384 current steps (14 bits, only for MT6372) in exponential or linear
+  mapping curves.
+
+allOf:
+  - $ref: common.yaml#
+
+properties:
+  compatible:
+    enum:
+      - mediatek,mt6370-backlight
+      - mediatek,mt6372-backlight
+
+  default-brightness:
+    minimum: 0
+
+  max-brightness:
+    minimum: 0
+
+  enable-gpios:
+    description: External backlight 'enable' pin
+    maxItems: 1
+
+  mediatek,bled-pwm-enable:
+    description: |
+      Enable external PWM input for backlight dimming
+    type: boolean
+
+  mediatek,bled-pwm-hys-enable:
+    description: |
+      Enable the backlight input-hysteresis for PWM mode
+    type: boolean
+
+  mediatek,bled-pwm-hys-input-th-steps:
+    $ref: /schemas/types.yaml#/definitions/uint8
+    enum: [1, 4, 16, 64]
+    description: |
+      The selection of the upper and lower bounds threshold of backlight
+      PWM resolution. If we choose selection 64, the variation of PWM
+      resolution needs more than 64 steps.
+
+  mediatek,bled-ovp-shutdown:
+    description: |
+      Enable the backlight shutdown when OVP level triggered
+    type: boolean
+
+  mediatek,bled-ovp-microvolt:
+    enum: [17000000, 21000000, 25000000, 29000000]
+    description: |
+      Backlight OVP level selection.
+
+  mediatek,bled-ocp-shutdown:
+    description: |
+      Enable the backlight shutdown when OCP level triggerred.
+    type: boolean
+
+  mediatek,bled-ocp-microamp:
+    enum: [900000, 1200000, 1500000, 1800000]
+    description: |
+      Backlight OC level selection.
+
+  mediatek,bled-exponential-mode-enable:
+    description: |
+      Enable the exponential mode of backlight brightness. If this property
+      is not enabled, the default is to use linear mode.
+    type: boolean
+
+  mediatek,bled-channel-use:
+    $ref: /schemas/types.yaml#/definitions/uint8
+    description: |
+      Backlight LED channel to be used.
+      Each bit mapping to:
+        - 0: CH4
+        - 1: CH3
+        - 2: CH2
+        - 3: CH1
+    minimum: 1
+    maximum: 15
+
+if:
+  properties:
+    compatible:
+      contains:
+        const: mediatek,mt6372-backlight
+
+then:
+  properties:
+    default-brightness:
+      maximum: 16384
+
+    max-brightness:
+      maximum: 16384
+
+else:
+  properties:
+    default-brightness:
+      maximum: 2048
+
+    max-brightness:
+      maximum: 2048
+
+required:
+  - compatible
+  - mediatek,bled-channel-use
+
+additionalProperties: false