Hi Daniel, Pavel, 2017-06-28 15:30 GMT+02:00 Pavel Machek <[email protected]>: > On Wed 2017-06-28 13:16:31, Enric Balletbo i Serra wrote: >> From: huang lin <[email protected]> >> >> Add a pwm-delay-us property to specify the delay between setting an >> initial (non-zero) PWM value and enabling the backlight, and also the >> delay between disabling the backlight and setting PWM value to 0. > > > >> Signed-off-by: huang lin <[email protected]> >> Signed-off-by: Enric Balletbo i Serra <[email protected]> >> --- >> Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt | 4 ++++ >> 1 file changed, 4 insertions(+) >> >> diff --git >> a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt >> b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt >> index 764db86..f75b08f 100644 >> --- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt >> +++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt >> @@ -17,6 +17,9 @@ Optional properties: >> "pwms" property (see PWM binding[0]) >> - enable-gpios: contains a single GPIO specifier for the GPIO which >> enables >> and disables the backlight (see GPIO binding[1]) >> + - pwm-delay-us: delay between setting an initial (non-zero) PWM value and >> + enabling the backlight, and also the delay between >> disabling >> + the backlight and setting PWM value to 0. >> > >> If is safe to assume power-on delay and power-off delay will be the same? >> >> I've only took a quick look but several backlight controllers support >> asymetric power-on/off sequences..
Daniel, right the ones I checked are symmetric but asymmetric timings are possible I guess, so I think now that specify the two delays is more accurate, maybe the binding should be something like this? pwm-delay-us = <delay_before_on delay_after_off>; > I understood it as "you set PWM and it takes a while for display to > light up" > but that's not correct. Changelog from second patch makes it > clear. Please > clarify it here, too. Pavel, oh, your dude is interesting ... That's the idea, the sequence is: Power on, you set the PWM signal, wait a bit and set the LED_EN signal. Power off, you clear the LED_EN signal, wait a bit and stop the PWM signal. Note that the patch inverts the sequence, before this patch first you set LED_EN signal and then the PWM signal I assumed that the sequence was wrong but maybe I'm mistaken and there are some panels that follow the original sequence. On the few panels I checked the power on/off sequence is how I described above, i.e. see [1] p. 17, the sequence is first PWM and then LED_EN. I'll take a look at other panel datasheets, or if you know one, could you provide me the datasheet? Thanks, [1] http://www.jxlcd.com/Upload/PicFiles/N116BGE-L41.pdf > > Pavel > -- > (english) http://www.livejournal.com/~pavelmachek > (cesky, pictures) > http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
