[Bug 78653] Backlight control broken on Dell XPS M1330 w/ kernel >= 3.14.1

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=78653

--- Comment #4 from Mikkel Oscar Lyderik <mikkeloscar at gmail.com> ---
(In reply to comment #3)
> (In reply to comment #2)
> > I finally got some time to do a bit of debugging.
> > 
> > Applying this hack: https://bugs.freedesktop.org/show_bug.cgi?id=76276#c15
> > and only this (to 3.15-rc6) solves the problem for me.
> 
> And backlight control works with that? What do you have in
> /sys/class/backlight?
> 
> The VBT says we should register backlight for that, but then it doesn't
> work. Hmm.

Yeah I don't have intel_backlight there.

with kernel 3.15-rc6 and the hack applied I have:

$ ls -l /sys/class/backlight/
total 0
lrwxrwxrwx 1 root root 0 May 27 16:42 acpi_video0 ->
../../devices/pci0000:00/0000:00:02.0/backlight/acpi_video0



With kernel 3.13.8 (before regression) I have:

$ ls -l
total 0
lrwxrwxrwx 1 root root 0 May 27 16:44 acpi_video0 ->
../../devices/pci0000:00/0000:00:02.0/backlight/acpi_video0
lrwxrwxrwx 1 root root 0 May 27 16:44 intel_backlight ->
../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight

Backlight control (Fn+ArrowUp/Down) works on both of those setups, but it
breaks when the 3.15-rc6+hack kernel is suspended and woken up again.

Do you need any other infomation?

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