Re : Re: Commit 76c2ff3e broke backlight on Chromebook snow

[Guillaume GARDET]

Hi Dario,

----- Dario Binacchi <dariobin at libero.it> a écrit :
> Hi Guillaume,
> 
> > Il 21/10/2021 16:47 Guillaume GARDET <guillaume.gardet at free.fr> ha scritto:
> > 
> >  
> > Hi,
> > 
> > Commit 76c2ff3e [0] broke backlight on Chromebook snow.
> > A revert on top of 2021.10 restores the backlight.
> > Not sure why it breaks on Chromebook snow yet. Dario, any idea how to fix this?
> 
> Is it possible that max_level is equal to min_level and therefore division 
> by zero is done?

I do not think so, because u-boot does not crash and the DTS file has multiple levels:
https://source.denx.de/u-boot/u-boot/-/blob/master/arch/arm/dts/exynos5250-snow.dts#L243

I think the problem occurs when 'cur_level == max_level', which is also the default value in the DTS.
If I change the default-brightness-level to 6 (instead of 7), then the backlight works again, which would confirm the assumption above.
pwm_backlight_set_brightness seems to set cur_level to max value by default. Maybe the driver thinks there is nothing to do, since current level is also the desired level?


Cheers,
Guillaume


> 
> Thanks and regards,
> Dario
> > 
> > Cheers,
> > Guillaume