[Bug 87286] [i915 intel_backlight] can't regulate brightness at GDM login prompt if HDMI monitor connected

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=87286

jre.winesim at gmail.com changed:

           What    |Removed                     |Added
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             Status|NEEDINFO                    |NEW

--- Comment #8 from jre.winesim at gmail.com ---
(In reply to Jani Nikula from comment #5)
> If you boot without HDMI, ensure backlight control works, then hotplug HDMI,
> does the backlight control cease to work?

Yes, without it works, after hotpluging it stops working. 


> Vice versa, if you boot with HDMI, confirm the bug is present, then unplug
> HDMI ,does the problem go away?

No, it doesn't work even after unpluging.


Just to clarify: with "does not work" I mean the backlight control OSD bar
moves, but only between 0 and about 5%. This has no practical effect
(especially not if the screen is dimmed to complete black as it was with kernel
3.16).


I successfully tested the attached patch which fixes the issue by disabling the
native backlight (based upon a patch by Aaron Lu for a similar bug (84561) for
*another* product).
I can't judge if this is sufficient, or if we should try to fix
intel_backlight. For the latter I'll also include the output of acpidump.


Thanks again
Jens Reyer

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