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. -- 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
