On Wed, Sep 26, 2012 at 22:19:49, Thierry Reding wrote: > 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. In non-DT case lth_brightness is required. But for DT we have options with/without lth_brightness support. In case if patch is dropped, user has to put proper brightness-levels (brightness-levels DT parameters should be specified considering the low-threshold values) Meanwhile I had submitted another version yesterday (with more documentation) [PATCH v3] pwm_backlight: Add device tree support for Low Threshold Brightness https://lkml.org/lkml/2012/9/26/271 Thierry, Can you please confirm the acceptance/rejection of the patch? This will help me to submit the backlight DT blob for AM335x platform. 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
