Pedro Marques, do any of the following provide a WORKAROUND via https://wiki.ubuntu.com/Kernel/Debugging/Backlight#Testing_for_a_work_around ?
For now, don't worry about attaching any debugging information requested in the article. ** Tags added: kernel-bug-exists-upstream kernel-bug-exists- upstream-3.18-rc7 -- 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/1397088 Title: 1002:6740 [iMac12,2] No brightness control Status in linux package in Ubuntu: Incomplete Bug description: Hello, I have no brightness control on imac 27 Core i5-2500S (poduct model: imac 12.2) running ubuntu trysty with xorg video ati driver. tried to use fglrx proprietary drivers, and end up with black screen and unable to boot. i only needed to low down brightness a little.. --- ApportVersion: 2.14.1-0ubuntu3.5 Architecture: amd64 AudioDevicesInUse: USER PID ACCESS COMMAND /dev/snd/controlC1: pfmarques 2190 F.... pulseaudio /dev/snd/controlC0: pfmarques 2190 F.... pulseaudio CRDA: country AW: (2402 - 2482 @ 40), (N/A, 20) (5170 - 5250 @ 40), (N/A, 20) (5250 - 5330 @ 40), (N/A, 20), DFS (5490 - 5710 @ 40), (N/A, 27), DFS DistroRelease: Ubuntu 14.04 HibernationDevice: RESUME=UUID=0c9bef7b-65b8-41bf-9548-6cf11bdd4059 InstallationDate: Installed on 2014-11-25 (5 days ago) InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2) MachineType: Apple Inc. iMac12,2 Package: linux (not installed) ProcFB: 0 inteldrmfb 1 radeondrmfb ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-40-generic.efi.signed root=UUID=dba8f74a-366d-4de8-862c-f0118c556c07 ro quiet splash vt.handoff=7 ProcVersionSignature: Ubuntu 3.13.0-40.69-generic 3.13.11.10 PulseList: Error: command ['pacmd', 'list'] failed with exit code 1: Home directory not accessible: Permission denied No PulseAudio daemon running, or not running as session daemon. RelatedPackageVersions: linux-restricted-modules-3.13.0-40-generic N/A linux-backports-modules-3.13.0-40-generic N/A linux-firmware 1.127.8 Tags: trusty Uname: Linux 3.13.0-40-generic x86_64 UpgradeStatus: No upgrade log present (probably fresh install) UserGroups: WifiSyslog: Dec 1 11:54:46 pfmarques-iMac wpa_supplicant[992]: message repeated 75 times: [ wlan0: CTRL-EVENT-SCAN-STARTED ] Dec 1 11:54:49 pfmarques-iMac wpa_supplicant[992]: nl80211: send_and_recv->nl_recvmsgs failed: -33 Dec 1 11:55:49 pfmarques-iMac wpa_supplicant[992]: wlan0: CTRL-EVENT-SCAN-STARTED Dec 1 12:01:14 pfmarques-iMac kernel: [ 5030.247003] perf samples too long (2512 > 2500), lowering kernel.perf_event_max_sample_rate to 50000 Dec 1 12:08:29 pfmarques-iMac kernel: [ 5465.506679] systemd-hostnamed[7862]: Warning: nss-myhostname is not installed. Changing the local hostname might make it unresolveable. Please install nss-myhostname! _MarkForUpload: True dmi.bios.date: 01/24/12 dmi.bios.vendor: Apple Inc. dmi.bios.version: IM121.88Z.0047.B1F.1201241648 dmi.board.name: Mac-942B59F58194171B dmi.board.vendor: Apple Inc. dmi.board.version: iMac12,2 dmi.chassis.type: 13 dmi.chassis.vendor: Apple Inc. dmi.chassis.version: Mac-942B59F58194171B dmi.modalias: dmi:bvnAppleInc.:bvrIM121.88Z.0047.B1F.1201241648:bd01/24/12:svnAppleInc.:pniMac12,2:pvr1.0:rvnAppleInc.:rnMac-942B59F58194171B:rvriMac12,2:cvnAppleInc.:ct13:cvrMac-942B59F58194171B: dmi.product.name: iMac12,2 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/1397088/+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