Re: [PATCH] dt-bindings: backlight: Convert common backlight bindings to DT schema

On Fri, Jun 19, 2020 at 11:53:41PM +0200, Sam Ravnborg wrote:

...

diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.yaml b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.yaml new file mode 100644 index 000000000000..7e1f109a38a4 --- /dev/null +++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.yaml @@ -0,0 +1,98 @@ +# SPDX-License-Identifier: GPL-2.0-only +%YAML 1.2 +--- +$id: http://devicetree.org/schemas/leds/backlight/pwm-backlight.yaml# +$schema: http://devicetree.org/meta-schemas/core.yaml#

+title: pwm-backlight bindings

+maintainers:

• • Lee Jones lee.jones@linaro.org
• • Daniel Thompson daniel.thompson@linaro.org
• • Jingoo Han jingoohan1@gmail.com

+properties:

• compatible:
• const: pwm-backlight
• pwms:
• maxItems: 1
• pwm-names: true
• power-supply:
• description: regulator for supply voltage
• enable-gpios:
• description: Contains a single GPIO specifier for the GPIO which enables

•  and disables the backlight
  

• maxItems: 1
• post-pwm-on-delay-ms:
• description: Delay in ms between setting an initial (non-zero) PWM and

•  enabling the backlight using GPIO.
  

• pwm-off-delay-ms:
• description: Delay in ms between disabling the backlight using GPIO

•  and setting PWM value to 0.
  

• brightness-levels:
• description: Array of distinct brightness levels. Typically these are

•  in the range from 0 to 255, but any range starting at 0 will do. The
  

•  actual brightness level (PWM duty cycle) will be interpolated from
  

•  these values. 0 means a 0% duty cycle (darkest/off), while the last
  

•  value in the array represents a 100% duty cycle (brightest).
  

• $ref: /schemas/types.yaml#/definitions/uint32-array
• default-brightness-level:
• description: The default brightness level (index into the array defined

•  by the "brightness-levels" property).
  

• $ref: /schemas/types.yaml#/definitions/uint32

Same comment as before...

Sorry the "ditto" meant I didn't thing about PWM as much as I should have.

The situation for PWM is a little different to LED. That's mostly because we decided not to clutter the LED code with "num-interpolated-steps".

The PWM code implements the default-brightness-level as an index into the brightness array *after* it has been expanded using interpolation. In other words today Linux treats the default-brightness-level more like[1].

description: The default brightness level. When num-interpolated-steps is not set this is simply an index into the array defined by the "brightness-levels" property. If num-interpolated-steps is set the brightness array will be expanded by interpolation before we index to get a default level.

This is the best I have come up with so far... but I concede it still lacks elegance.

Daniel.

[1] I don't know my way round the BSD code bases to be sure what they do... I did a couple of web searches but didn't pull up anything definitive.

...

• num-interpolated-steps:
• description: 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.
  

• $ref: /schemas/types.yaml#/definitions/uint32

+dependencies:

• default-brightness-level: [brightness-levels]
• num-interpolated-steps: [brightness-levels]

+required:

• • compatible
• • pwms
• • power-supply

+additionalProperties: false

+examples:

• • |
• backlight {

•    compatible = "pwm-backlight";
  

•    pwms = <&pwm 0 5000000>;
  

•    brightness-levels = <0 4 8 16 32 64 128 255>;
  

•    default-brightness-level = <6>;
  

•    power-supply = <&vdd_bl_reg>;
  

•    enable-gpios = <&gpio 58 0>;
  

•    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>;
  

• };

+...

2.25.1

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