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 <bonb...@linux-vserver.org> 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 <petriho...@yahoo.com> Tested-by: Petri Hodju <petriho...@yahoo.com> Cc: Bjorn Helgaas <bhelg...@google.com> Cc: Matthew Garrett <matthew.garr...@nebula.com> Signed-off-by: Bruno Prémont <bonb...@linux-vserver.org> Signed-off-by: Darren Hart <dvh...@linux.intel.com> :040000 040000 b9fa60f95e23f0d9916f92df51b95e4b73c80ecf d842064bce0c54557a3b1dd9dcd357f0e204dde1 M drivers ** Bug watch added: Linux Kernel Bug Tracker #86121 http://bugzilla.kernel.org/show_bug.cgi?id=86121 ** Attachment added: "log.txt" https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1512691/+attachment/4567749/+files/log.txt -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1512691 Title: [MacBookPro11,3] Backlight control does not work, but there are entries in /sys/class/backlight Status in linux package in Ubuntu: Triaged Bug description: 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. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1512691/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp