| Message ID | 20180110223046.17696-3-enric.balletbo@collabora.com |
|---|---|
| State | Changes Requested, archived |
| Headers | show |
| Series | backlight: pwm_bl: support linear interpolation and brightness to human eye | expand |
On Wed, Jan 10, 2018 at 11:30:44PM +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> > --- > .../bindings/leds/backlight/pwm-backlight.txt | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > > diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > index 310810906613..605432c910c5 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 +44,19 @@ 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 65535>; > + num-interpolated-steps = <4096>; How does this make sense with only 2 defined levels other than having fewer steps? I thought the purpose of this was to have a piecewise linear curve. > + default-brightness-level = <6>; Aren't valid values 0, 16, 32, 48, etc.? Rob -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Jan 19, 2018 at 02:52:49PM -0600, Rob Herring wrote: > On Wed, Jan 10, 2018 at 11:30:44PM +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> > > --- > > .../bindings/leds/backlight/pwm-backlight.txt | 21 +++++++++++++++++++++ > > 1 file changed, 21 insertions(+) > > > > diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt > > index 310810906613..605432c910c5 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 +44,19 @@ 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 65535>; > > + num-interpolated-steps = <4096>; > > How does this make sense with only 2 defined levels other than having > fewer steps? I thought the purpose of this was to have a piecewise > linear curve. It's not wrong as such, this is how a device with a linear (or nearly linear) response could be compactly described. Nevertheless I agree! An example with a small but realistic curve would be better... we know that copy 'n paste exists so I'd rather see a simple curve than no curve. Daniel. > > + default-brightness-level = <6>; > > Aren't valid values 0, 16, 32, 48, etc.? > > Rob -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
2018-01-22 10:16 GMT+01:00 Daniel Thompson <daniel.thompson@linaro.org>: > On Fri, Jan 19, 2018 at 02:52:49PM -0600, Rob Herring wrote: >> On Wed, Jan 10, 2018 at 11:30:44PM +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> >> > --- >> > .../bindings/leds/backlight/pwm-backlight.txt | 21 +++++++++++++++++++++ >> > 1 file changed, 21 insertions(+) >> > >> > diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt >> > index 310810906613..605432c910c5 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 +44,19 @@ 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 65535>; >> > + num-interpolated-steps = <4096>; >> >> How does this make sense with only 2 defined levels other than having >> fewer steps? I thought the purpose of this was to have a piecewise >> linear curve. > > It's not wrong as such, this is how a device with a linear (or nearly > linear) response could be compactly described. > > Nevertheless I agree! An example with a small but realistic curve > would be better... we know that copy 'n paste exists so I'd rather > see a simple curve than no curve. > Makes sense, I'll put a better example on next series. Thanks for the review. - Enric > > Daniel. > > >> > + default-brightness-level = <6>; >> >> Aren't valid values 0, 16, 32, 48, etc.? >> >> Rob -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt index 310810906613..605432c910c5 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 +44,19 @@ 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 65535>; + num-interpolated-steps = <4096>; + 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>; + };
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> --- .../bindings/leds/backlight/pwm-backlight.txt | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+)