[Bug 81762] New: Backlight keys on ASUS UX301

[bugzilla-daemon at freedesktop.org]

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

          Priority: medium
            Bug ID: 81762
                CC: intel-gfx-bugs at lists.freedesktop.org
          Assignee: intel-gfx-bugs at lists.freedesktop.org
           Summary: Backlight keys on ASUS UX301
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: jwboyer at fedoraproject.org
          Hardware: Other
            Status: NEW
           Version: unspecified
         Component: DRM/Intel
           Product: DRI

I recently received an ASUS UX301 laptop.  After installing Fedora 21 and then
using a git kernel (v3.16-rc5-152-g59ca9ee42838) things worked well except the
brightness keys.  (The keys didn't work in the 3.11.10 kernel, or any other
kernel I tried either.)  After some debugging, I figured out the ACPI events
for the keys are never actually being sent to the kernel at all.

Matthew Garrett and I poked at this over the course of a few days and found a
few things.

1) _DOD is returning 16 devices.  The last device has a device_id of 0x400 and
appears to be the device being used.

2) intel_didl_outputs is only looping through and setting up 8 devices in didl.
 intel_setup_cadls is looping through and blindly assigning the id from didl[i]
to cadl[i] even though the active device might not be in the first 8 devices. 
This probably works on most machines because DIDL is only 8 in length.

3) The AML from this machine is a bit odd, in that it references methods from
the LCDD device, which tries to figure out which active device to return in
it's CDDS method.  Since the active device in question isn't listed in any of
the CADL entries, the AML method fails and no events are sent to the kernel.

4) If I blindly slam the returned device_id (0x400) into cadl[0], the
brightness keys work as expected with the backlight being adjusted and the OSD
in GNOME popping up.  Clearly that isn't a solution, but it does lead to some
hints as to what the problem is.

The acpidump output for the machine can be found here:
https://jwboyer.fedorapeople.org/pub/acpi.dump

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