[Bug 81762] Backlight keys on ASUS UX301

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=81762

--- Comment #6 from Ondrej Sury <ondrej at sury.org> ---
I have an ASUS UX301LAA notebook running 3.16.5 (and 3.17) kernel and the
backlight keys also doesn't work for me.

But - it looks like there might be some clash between backlight providers,
there are two providers: acpi_nb_wmi (type:platform) and intel_backlight
(type:raw)

# ls -ld /sys/class/backlight/*
lrwxrwxrwx. 1 root root 0 Nov  2 15:12 /sys/class/backlight/asus-nb-wmi ->
../../devices/platform/asus-nb-wmi/backlight/asus-nb-wmi
lrwxrwxrwx. 1 root root 0 Nov  2 15:12 /sys/class/backlight/intel_backlight ->
../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight

Manipulating brightness manually in intel_backlight in fact does change the
brightness and I can modify brightness with hacked gsd-backlight-helper that
prefers type=raw instead of type=platform using the slider controls in
gnome-shell.

I can confirm that keyboard (Fn-F5 and Fn-F6) does not work and they also don't
generated any events in xev (keyboard brightness keys do).

There was an Ubuntu patch that added enable_backlight=0 option to the module,
so it can be disabled, but alas it doesn't apply on 3.16 anymore.  I think it
might be usefull to have such option to at least test whether disabling
intel_backlight and letting asus_nb_wmi handle the backlight helps.  Not sure
whether this is bug in i915 or asus_nb_wmi though (or both).

Not sure whether this was helpful, but at least you have one more person to
help with debugging.

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