[PATCH 3/5 v7] dt-bindings: input: pwm-beeper: add documentation for volume devcetree bindings

[Manuel Traut <manuel.traut@mt.com>]

This patch adds the documentation for the devicetree bindings to set
the volume levels.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Manuel Traut <manuel.traut@mt.com>
Acked-by: Rob Herring <robh@kernel.org>
---
 .../devicetree/bindings/input/pwm-beeper.yaml | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/Documentation/devicetree/bindings/input/pwm-beeper.yaml b/Documentation/devicetree/bindings/input/pwm-beeper.yaml
index 24a40f0f77c1..fe1bbc10147b 100644
--- a/Documentation/devicetree/bindings/input/pwm-beeper.yaml
+++ b/Documentation/devicetree/bindings/input/pwm-beeper.yaml
@@ -28,6 +28,23 @@ properties:
 	beeper-hz:
 		description: bell frequency in Hz
 
+
+	volume-levels:
+		description: >
+			Array of PWM duty cycle values that correspond to
+			linear volume levels. These need to be in the range of
+			0 to 500, while 0 means 0% duty cycle (mute) and 500
+			means 50% duty cycle (max volume).
+			Please note that the actual volume of most beepers is
+			highly non-linear, which means that low volume levels
+			are probably somewhere in the range of 1 to 30 (0.1-3%
+			duty cycle).
+
+	default-volume-level:
+		description: >
+			The default volume level (index into the array defined
+			by the "volume-levels" property).
+
 required:
 	- compatible
 	- pwms
@@ -45,4 +62,6 @@ examples:
 			compatible = "pwm-beeper";
 			pwms = <&pwm0>;
 			amp-supply = <&beeper_amp>;
+			volume-levels = <0 8 20 40 500>;
+			default-volume-level = <4>;
 		};
-- 
2.39.0