On Fri, Sep 28, 2012 at 11:15:48, Thierry Reding wrote: > On Thu, Sep 27, 2012 at 02:33:09PM -0700, Andrew Morton wrote: > > On Wed, 26 Sep 2012 20:17:07 +0530 > > "Philip, Avinash" <avinashphilip@xxxxxx> wrote: > > > > > Some back lights perform poorly when driven by a PWM with a short > > > duty-cycle. For such devices, the low threshold can be used to specify a > > > lower bound for the duty-cycle and should be chosen to exclude the > > > problematic range. > > > > > > Add device tree probing support for lth_brightness putting > > > low-threshold-brightness as optional property. > > > > > > ... > > > > > > --- a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt > > > +++ b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt > > > @@ -14,6 +14,15 @@ Required properties: > > > Optional properties: > > > - pwm-names: a list of names for the PWM devices specified in the > > > "pwms" property (see PWM binding[0]) > > > + - low-threshold-brightness: brightness threshold low level. Low threshold > > > + brightness set to value so that backlight present on low end of > > > + brightness. > > > + Some panels, backlight would absent if duty percentage of PWM wave is less > > > + than certain level (say 20%). By setting low-threshold-brightness to a > > > + value above (percentage of brightness-levels max) 50 (20% of 255, if 255 > > > + is max). On setting low-threshold-brightness, range of brightness-levels > > > + is calculated in a region of low-threshold-brightness to brightness-levels > > > + max. > > > > hoo boy, that's hard to follow. How does this look? > > > > --- a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt~pwm_backlight-add-device-tree-support-for-low-threshold-brightness-fix > > +++ a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt > > @@ -14,15 +14,15 @@ Required properties: > > Optional properties: > > - pwm-names: a list of names for the PWM devices specified in the > > "pwms" property (see PWM binding[0]) > > - - low-threshold-brightness: brightness threshold low level. Low threshold > > - brightness set to value so that backlight present on low end of > > - brightness. > > - Some panels, backlight would absent if duty percentage of PWM wave is less > > - than certain level (say 20%). By setting low-threshold-brightness to a > > - value above (percentage of brightness-levels max) 50 (20% of 255, if 255 > > - is max). On setting low-threshold-brightness, range of brightness-levels > > - is calculated in a region of low-threshold-brightness to brightness-levels > > - max. > > + - low-threshold-brightness: brightness threshold low level. Sets the lowest > > + brightness value. > > + On some panels the backlight misbehaves if the duty cycle percentage of the > > + PWM wave is less than a certain level (say 20%). In this example the user > > + can set low-threshold-brightness to a value above 50 (ie, 20% of 255), thus > > + preventing the PWM duty cycle from going too low. > > + On setting low-threshold-brightness the range of brightness levels is > > + calculated in the range low-threshold-brightness to the maximum value in > > + brightness-levels, described above. > > > > [0]: Documentation/devicetree/bindings/pwm/pwm.txt > > > > > > > > Also, I'm wondering if we really needed a new property - couldn't one > > do this simply by setting brightness-levels to 50..255? > > Yes. This was discussed in the thread that followed the posting of this > patch's v2. We've decided to drop it and go with brightness-levels only > for device tree data. Eventually all existing users should convert to > that as well so we can remove some of the cruft from the platform data > up. Andrew/Thierry, It was decided that patch as dropped and still see it in linux-next. http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git;a=commit;h=1801ff7f87131190b0a469c26bd7c829601e198c Thanks Avinash > > Thierry > -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
