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. But then, in the email you linked to, what does "But brightness-levels won't be uniformly divided" mean? Why would doing the calculation at run-time be any better than simply putting the correct values into brightness-levels in the first place? Either way, the DT binding should explain exactly what this value is used for, and how it affects the interpretation of values in brightness-levels. -- 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
