[Bug 70256] [snb] initial backlight brightness is zero

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=70256

--- Comment #15 from Kirill Tkhai <tkhai at yandex.ru> ---
(In reply to comment #13)
> (In reply to comment #12)
> > What if you try the acpi_osi="!Windows 2012" kernel parameter?
> 
> Hmm, this was sandy bridge though... have you upgraded your bios? (I am not
> implying you should, I'm merely asking.)

No yet. I'll try to do upgrade too.

(In reply to comment #14)
> Another module parameter to try: video.use_bios_initial_backlight=0.

Thanks a lot! This solves the problem. Initial values are maximum:

$ cat /sys/class/backlight/acpi_video0/brightness
100

$ cat /sys/class/backlight/intel_backlight/brightness
4845

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