[PATCH v3 2/4] dt-bindings: pwm-backlight: add a num-interpolation-steps property.

Enric Balletbo i Serra
2018-02-08T11:30:45Z

The num-interpolated-steps property specifies the number of
interpolated steps between each value of brightness-level table. This is
useful for high resolution PWMs to not have to list out every possible
value in the brightness-level array.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
---
Changes since v2:
- Add Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Changes since v1:
- Add an example with a small but realistic curve. Suggested by Rob and
Daniel

.../bindings/leds/backlight/pwm-backlight.txt | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)

diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
index 310810906613..ce9b5746b774 100644
--- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
+++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
@@ -21,6 +21,11 @@ Optional properties:
and enabling the backlight using GPIO.
- pwm-off-delay-ms: Delay in ms between disabling the backlight using GPIO
and setting PWM value to 0.
+ - num-interpolated-steps: Number of interpolated steps between each value
+ of brightness-levels table. This way a high
+ resolution pwm duty cycle can be used without
+ having to list out every possible value in the
+ brightness-level array.

[0]: Documentation/devicetree/bindings/pwm/pwm.txt
[1]: Documentation/devicetree/bindings/gpio/gpio.txt
@@ -39,3 +44,17 @@ Example:
post-pwm-on-delay-ms = <10>;
pwm-off-delay-ms = <10>;
};
+
+Example using num-interpolation-steps:
+
+ backlight {
+ compatible = "pwm-backlight";
+ pwms = <&pwm 0 5000000>;
+
+ brightness-levels = <0 2048 4096 8192 16384 65535>;
+ num-interpolated-steps = <2048>;
+ default-brightness-level = <4096>;
+
+ power-supply = <&vdd_bl_reg>;
+ enable-gpios = <&gpio 58 0>;
+ };
--
2.15.1