[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 #23 from Sylvain Pasche <sylvain.pasche at gmail.com> ---
(In reply to Hans de Goede from comment #22)
> Sylvain, do you still have an xorg.conf file hanging around telling the
> intel ddx to use the intel_backlight interface? Can you try running the
> latest Fedora-22 kernel without such a file and without any special kernel
> commandline arguments? If that does not help then I'm afraid I'm all out of
> ideas and one of the intel devs will need to look at reg-dumps and figure
> out what exactly is going on at a much lower level.

Hi Hans. I didn't have a xorg.conf file lying around. In fact, I also tested
with the Fedora Workstation 22 installation DVD to make sure that I have
nothing interfering. In this situation, I have the behavior described above:
* two backlight interfaces are exposed: acpi_video0 and intel_backlight
* they both work after boot
* after suspend / resume, only the intel_backlight interface works
* backlight is turned on after boot or resume

Maybe we could implement the workaround in user space: set a udev device
property telling Gnome that it should ignore the acpi_video0 interface and fall
back to the intel_backlight one.

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