Hi Dario,

----- Dario Binacchi dariobin@libero.it a écrit :

Hi Guillaume,

...

Il 21/10/2021 16:47 Guillaume GARDET guillaume.gardet@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-s...

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

Hi,

On Sat, 23 Oct 2021 at 03:23, Dario Binacchi dariobin@libero.it wrote:

Hi Guillaume,

...

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

Hi Dario,

----- Dario Binacchi dariobin@libero.it a écrit :

...

Hi Guillaume,

...

Il 21/10/2021 16:47 Guillaume GARDET guillaume.gardet@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-s...

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.

I got this running in my lab now and sent a possible fix.

Regards, Simon

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?

[..]