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

[Dario Binacchi]

Hi Guillaume,

> Il 22/10/2021 14:34 Guillaume GARDET <guillaume.gardet at free.fr> ha scritto:
> 
>  
> 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.

I have set the default-brightness-level to max-level on my beaglebone board but the backlight works the same.
I didn't see any difference.

Thanks and regards
Dario

> 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