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

Message ID 20180208113032.27810-3-enric.balletbo@collabora.com
State Not Applicable, archived
Headers show
Series
  • backlight: pwm_bl: support linear interpolation and brightness to human eye
Related show

Commit Message

Enric Balletbo i Serra Feb. 8, 2018, 11:30 a.m.
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(+)

Comments

Rob Herring Feb. 18, 2018, 10:49 p.m. | #1
On Thu, Feb 08, 2018 at 12:30:30PM +0100, Enric Balletbo i Serra wrote:
> 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(+)

Reviewed-by: Rob Herring <robh@kernel.org>
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Patch

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>;
+	};