[Bug 82634] [snb] backlight issue on TOSHIBA PORTEGE R830 after suspend/resume

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=82634

--- Comment #16 from Hans de Goede <jwrdegoede at fedoraproject.org> ---
(In reply to Sylvain Pasche from comment #15)

<snip>

> I can change the brightness on both.
> 
> After a suspend+resume:
> 
>   The backlight is turned on.
>   changing brightness of acpi_video0 has no effect
>   changing brightness of intel_backlight works

Ok, so it seems that the 2 backlight control methods are getting in each others
way, and disabling the acpi_video0 one is not an option as then the backlight
does not go back on after a suspend/resume. So lets try disabling the intel
backlight control.

I've done a scratch kernel build for F-22 with a patch which adds a module
param which allows you to tell the intel driver to not touch the backlight:

http://koji.fedoraproject.org/koji/taskinfo?taskID=9865887

Please install this kernel and then boot into it with:
"i915.enable_backlight_control=0" (and no other backlight related options) 
added to the kernel commandline, then do:

ls /sys/class/backlight

And you should only see acpi_video0 there, then try if backlight control works,
then suspend/resume and check if backlight control still works.

I'll attach the patch I did here in case anyone following this wants to take a
look, I'll submit it upstream once we've confirmed that it helps :)

Regards,

Hans

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