[MacBookPro11,3] Backlight control does not work, but there are entries in /sys/class/backlight

[Gaele Strootman]

Backlight control stopped working after upgrade from Vivid to Wily.

/sys/class/backlight/gmux_backlight$ grep . *
actual_brightness:16777215
bl_power:0
brightness:400
grep: device: Is a directory
max_brightness:-1
grep: power: Is a directory
grep: subsystem: Is a directory
type:platform

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: linux-image-4.2.0-16-generic 4.2.0-16.19
ProcVersionSignature: Ubuntu 4.2.0-16.19-generic 4.2.3
Uname: Linux 4.2.0-16-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.19.1-0ubuntu4
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC1: gaele 2525 F.... pulseaudio
 /dev/snd/controlC0: gaele 2525 F.... pulseaudio
CurrentDesktop: Unity
Date: Tue Nov 3 13:44:25 2015
EcryptfsInUse: Yes
HibernationDevice: RESUME=UUID=716bc023-ef4e-436e-8e5b-5a1f548faef8
InstallationDate: Installed on 2015-04-26 (190 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
MachineType: Apple Inc. MacBookPro11,3
ProcFB: 0 nouveaufb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.2.0-16-generic.efi.signed root=UUID=38c8fe6d-3763-4619-a710-f65494173fe4 ro quiet splash libata.force=noncq vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-4.2.0-16-generic N/A
 linux-backports-modules-4.2.0-16-generic N/A
 linux-firmware 1.149
SourcePackage: linux
UpgradeStatus: Upgraded to wily on 2015-10-22 (11 days ago)
dmi.bios.date: 06/05/2015
dmi.bios.vendor: Apple Inc.
dmi.bios.version: MBP112.88Z.0138.B15.1506050548
dmi.board.asset.tag: Base Board Asset Tag#
dmi.board.name: Mac-2BD1B31983FE1663
dmi.board.vendor: Apple Inc.
dmi.board.version: MacBookPro11,3
dmi.chassis.type: 10
dmi.chassis.vendor: Apple Inc.
dmi.chassis.version: Mac-2BD1B31983FE1663
dmi.modalias: dmi:bvnAppleInc.:bvrMBP112.88Z.0138.B15.1506050548:bd06/05/2015:svnAppleInc.:pnMacBookPro11,3:pvr1.0:rvnAppleInc.:rnMac-2BD1B31983FE1663:rvrMacBookPro11,3:cvnAppleInc.:ct10:cvrMac-2BD1B31983FE1663:
dmi.product.name: MacBookPro11,3
dmi.product.version: 1.0
dmi.sys.vendor: Apple Inc.

[Gaele Strootman (gaele)]

Contrary to bug #1115555, nothing changes after changing the brightness in MacOSX and rebooting back into Ubuntu. I'm still at maximum brightness.

[Brad Figg (brad-figg)]

This change was made by a bot.

[Joseph Salisbury (jsalisbury)]

Would it be possible for you to test the latest upstream kernel? Refer to https://wiki.ubuntu.com/KernelMainlineBuilds . Please test the latest v4.3 kernel[0].

If this bug is fixed in the mainline kernel, please add the following tag 'kernel-fixed-upstream'.

If the mainline kernel does not fix this bug, please add the tag: 'kernel-bug-exists-upstream'.

Once testing of the upstream kernel is complete, please mark this bug as "Confirmed".

Thanks in advance.

[0] http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.3-unstable/

[penalvch (penalvch)]

Gaele Strootman, the next step is to fully commit bisect from kernel 3.19 to 4.2 in order to identify the last good kernel commit, followed immediately by the first bad one. This will allow for a more expedited analysis of the root cause of your issue. Could you please do this following https://wiki.ubuntu.com/Kernel/KernelBisection ?

Please note, finding adjacent kernel versions is not fully commit bisecting.

Thank you for your understanding.

Helpful bug reporting tips:
https://wiki.ubuntu.com/ReportingBugs

[Gaele Strootman (gaele)]

I tried a few kernels (4.0.0-2, 4.1.0-1, 4.2.0-7), installing linux-headers, linux-headers-generic and linux-image-generic. Booting into each of them left me with a non-working keyboard and mouse. Any suggestions?

[Gaele Strootman (gaele)]

Finally I found the courage to try commit bisecting the kernel. This is the result:

4eebd5a4e72697aac25a8a57d3f888a9d5f80370 is the first bad commit
commit 4eebd5a4e72697aac25a8a57d3f888a9d5f80370
Author: Bruno Prémont <email address hidden>
Date: Wed Mar 11 22:34:45 2015 +0100

    apple-gmux: lock iGP IO to protect from vgaarb changes

    As GMUX depends on IO for iGP to be enabled and active, lock the IO at
    vgaarb level. This should prevent GPU driver for dGPU to disable IO for
    iGP while it tries to own legacy VGA IO.

    This fixes usage of backlight control combined with closed nvidia
    driver on some Apple dual-GPU (intel/nvidia) systems.

    On those systems loading nvidia driver disables intel IO decoding,
    disabling the gmux backlight controls as a side effect.
    Prior to commits moving boot_vga from (optional) efifb to less optional
    vgaarb this mis-behavior could be avoided by using right kernel config
    (efifb enabled but vgaarb disabled).

    This patch explicitly does not try to trigger vgaarb changes in order
    to avoid confusing already running graphics drivers. If IO has been
    mis-configured by vgaarb gmux will thus fail to probe.
    It is expected to load/probe gmux prior to graphics drivers.

    Fixes: ce027dac592c0ada241ce0f95ae65856828ac450 # nvidia interaction
    Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=86121
    Reported-by: Petri Hodju <email address hidden>
    Tested-by: Petri Hodju <email address hidden>
    Cc: Bjorn Helgaas <email address hidden>
    Cc: Matthew Garrett <email address hidden>
    Signed-off-by: Bruno Prémont <email address hidden>
    Signed-off-by: Darren Hart <email address hidden>

:040000 040000 b9fa60f95e23f0d9916f92df51b95e4b73c80ecf d842064bce0c54557a3b1dd9dcd357f0e204dde1 M drivers

[Gaele Strootman (gaele)]

In case it is not immediately clear from the above: I'm using nouveau.

[penalvch (penalvch)]

Gaele Strootman, the issue you are reporting is an upstream one. Could you please report this problem following the instructions verbatim at https://wiki.ubuntu.com/Bugs/Upstream/kernel to the appropriate mailing list (TO Bruno Prémont, Bjorn Helgaas, Matthew Garrett, and Darren Hart CC platform-driver-x86)?

Please provide a direct URL to your post to the mailing list when it becomes available so that it may be tracked.

Thank you for your understanding.

[Gaele Strootman (gaele)]

http://www.spinics.net/lists/platform-driver-x86/msg08438.html