Document the device-tree binding of MediatTek display PWM.
The clock "main" and "mm" are used to generate PWM signals.
The PWM has one channel to control the backlight brightness for display.
It supports MT8173 and MT6595.

Change-Id: I194ca88b4e4cd01a28b8701e07e86ea6941e5292
Signed-off-by: YH Huang <redacted>
---
 .../devicetree/bindings/pwm/pwm-mtk-disp.txt       | 24 ++++++++++++++++++++++
 1 file changed, 24 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/pwm/pwm-mtk-disp.txt

diff --git a/Documentation/devicetree/bindings/pwm/pwm-mtk-disp.txt b/Documentation/devicetree/bindings/pwm/pwm-mtk-disp.txt
new file mode 100644
index 0000000..355b755
--- /dev/null
+++ b/Documentation/devicetree/bindings/pwm/pwm-mtk-disp.txt

@@ -0,0 +1,24 @@
+MediaTek display PWM controller
+
+Required properties:
+ - compatible: should be "mediatek,<name>-disp-pwm"
+   - "mediatek,mt8173-disp-pwm": found on mt8173 SoC
+   - "mediatek,mt6595-disp-pwm": found on mt6595 SoC
+ - reg: physical base address and length of the controller's registers
+ - #pwm-cells: must be 2. See pwm.txt in this directory for a description of
+   the cell format
+ - clocks: phandle and clock specifier of the PWM reference clock
+ - clock-names: must contain the following
+   - "main": clock used to generate PWM signals
+   - "mm": sync signals from the modules of mmsys
+
+Example:
+	pwm0: pwm at 1401e000 {
+		compatible = "mediatek,mt8173-disp-pwm",
+			     "mediatek,mt6595-disp-pwm";
+		reg = <0 0x1401e000 0 0x1000>;
+		#pwm-cells = <2>;
+		clocks = <&mmsys MM_DISP_PWM026M>,
+			 <&mmsys MM_DISP_PWM0MM>;
+		clock-names = "main", "mm";
+	};