On Wed, Sep 26, 2012 at 09:27:51AM -0600, Stephen Warren wrote: > On 09/25/2012 10:35 PM, Philip, Avinash wrote: > > On Tue, Sep 25, 2012 at 11:49:14, Stephen Warren wrote: > >> On 09/24/2012 10:29 PM, Philip, Avinash wrote: > >>> On Fri, Sep 21, 2012 at 23:13:39, Stephen Warren wrote: > >>>> On 09/21/2012 12:03 AM, Philip, Avinash wrote: > >>>>> Hi Stephen, > >>>>> > >>>>> On Fri, Sep 21, 2012 at 10:46:45, Stephen Warren wrote: > >>>>>> On 09/20/2012 10:51 PM, Philip, Avinash wrote: > >>>>>>> Some backlights 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. > >>>>>>> > >>>>>>> This patch adds support for an optional low-threshold-brightness > >>>>>>> property. > >>>>>> > >>>>>>> diff --git a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt > >>>>>> > >>>>>>> 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. > >>>>>> > >>>>>> For my education, why not just specify values above this value in the > >>>>>> brightness-levels array; how do those two interact? > >>>>> > >>>>> Please find details from > >>>>> https://lkml.org/lkml/2012/7/18/284 > >>>> > >>>> Hmm. That still doesn't really explain what this property does. > >>>> > >>>> I'm going to guess that if this property is present, and values in the > >>>> brightness-levels property get scaled between the > >>>> low-threshold-brightness and 255 instead of being used directly. > >>> > >>> This is correct. > >>> > >>>> But then, in the email you linked to, what does "But brightness-levels won't > >>>> be uniformly divided" mean? > >>> > >>> For some panels, backlight would absent on low end of brightness due to low > >>> percentage in duty_cycle. Consider following example where backlight absent > >>> for brightness levels from 0 - 51. > >>> > >>> pwms = <&pwm 0 50000>; > >>> brightness-levels = <0 51 53 56 62 75 101 152 255>; > >>> default-brightness-level = <6>; > >>> > >>> So in the example, brightness-levels are set to have values for backlight present. > >>> Here levels are not uniformly divided. > >> > >> So why not just change the values so they /are/ what you want? After > >> all, it's just data and you can put whatever values you want there. What > >> is preventing you from doing this? > > > > brightness_threshold_level was added to explore lth_brightness support already > > present in non-DT case. > > I understand that. Given my discussion above, I would advocate removing > lth_brightness from the non-DT case rather than adding it to the DT > case, since it seems entirely pointless. It is still required for the case where brightness levels are not used. So we can't drop it right away. I agree however that we should plan to get rid of the max_brightness and lth_brightness eventually. Since the DT bindings don't use it yet we should keep only the brightness levels. Once all users have been converted we can rename max_brightness to something like num_levels and remove lth_brightness. dft_brightness can probably be renamed to default_level. Thierry
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