On Mon, Jun 29, 2020 at 11:57:37AM -0600, Rob Herring wrote: > On Mon, Jun 22, 2020 at 10:57 AM Daniel Thompson > <daniel.thompson@xxxxxxxxxx> wrote: > > > > 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@xxxxxxxxxx> > > > > + - Daniel Thompson <daniel.thompson@xxxxxxxxxx> > > > > + - Jingoo Han <jingoohan1@xxxxxxxxx> > > > > + > > > > +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. > > Happy to add this or whatever folks want if there's agreement, but I > don't want to get bogged down on re-reviewing and re-writing the > binding on what is just a conversion. There's a mountain of bindings > to convert. The original explanation is ok, as pointed out by Daniel. So I suggest moving forward with that and then others can improve the descriptions later as necessary. Sam
