[PATCH 2/3 v6] input: pwm-beeper: add feature to set volume level

[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@exceet.de>
Acked-by: Rob Herring <robh@kernel.org>
---
 .../devicetree/bindings/input/pwm-beeper.txt          | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/Documentation/devicetree/bindings/input/pwm-beeper.txt b/Documentation/devicetree/bindings/input/pwm-beeper.txt
index 8fc0e48c20db..93cab5eee9f2 100644
--- a/Documentation/devicetree/bindings/input/pwm-beeper.txt
+++ b/Documentation/devicetree/bindings/input/pwm-beeper.txt
@@ -9,6 +9,15 @@ Required properties:
 Optional properties:
 - amp-supply: phandle to a regulator that acts as an amplifier for the beeper
 - beeper-hz:  bell frequency in Hz
+- volume-levels: 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: the default volume level (index into the
+      array defined by the "volume-levels" property)
 
 Example:
 
@@ -21,4 +30,6 @@ beeper {
 	compatible = "pwm-beeper";
 	pwms = <&pwm0>;
 	amp-supply = <&beeper_amp>;
+	volume-levels = <0 8 20 40 500>;
+	default-volume-level = <4>;
 };
-- 
2.39.0