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[fraktalek <1279569@xxxxxxxxxxxxxxxxxx>]

Thanks for commenting.

Actually, it seems that maybe the bug was just some temporary or
intermittent problem. Now my backlight controls work again, I didn't
change anything :-/ I'm running with the "thinkpad-
acpi.brightness_enable=1 acpi_backlight=vendor". I'll try without it
too.

If the problem persists I'll try the latest upstream kernel. I'll
comment again about the result. Thanks.

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https://bugs.launchpad.net/bugs/1279569

Title:
  Backlight control suddenly stops working on ThinkPad T420

Status in “linux” package in Ubuntu:
  Incomplete

Bug description:
  Backlight control with Fn+Home, Fn+End stopped working for me today
  out of nothing. I am not aware of any changes that might have caused
  it. I am installing updates as they come, so it could have been an
  update.

  I followed the guidelines at
  https://wiki.ubuntu.com/Kernel/Debugging/Backlight

  I can change brightness by writing to
  /sys/class/backlight/intel_backlight/brightness, for example echo 1000
  > /sys/class/backlight/intel_backlight/brightness

  None of the kernel parameters changed the behavior..., not even
  thinkpad-acpi.brightness_enable=1 acpi_backlight=vendor - that is even
  with these parameters the brightness control shortcuts don't work and
  changing brightness by writing to the above file does work. I am not
  aware of any brightness changing applet I could try. I'm using Gnome
  Shell if that matters.

  Let me know what I can do, thank you.

  ProblemType: Bug
  DistroRelease: Ubuntu 13.10
  Package: linux-image-3.11.0-15-generic 3.11.0-15.25
  ProcVersionSignature: Ubuntu 3.11.0-15.25-generic 3.11.10
  Uname: Linux 3.11.0-15-generic x86_64
  ApportVersion: 2.12.5-0ubuntu2.2
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC1:  jakub      2972 F.... pulseaudio
   /dev/snd/controlC0:  jakub      2972 F.... pulseaudio
  Date: Wed Feb 12 23:10:06 2014
  HibernationDevice: RESUME=UUID=9009e872-0f42-4632-bc0a-4a70931f9767
  InstallationDate: Installed on 2011-06-06 (982 days ago)
  InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release amd64 (20110427.1)
  MachineType: LENOVO 4180W1G
  MarkForUpload: True
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.11.0-15-generic root=UUID=e79e9934-9ad4-4091-8b9d-2ef7b1dba68e ro video.use_bios_initial_backlight=0 quiet splash vt.handoff=7
  RelatedPackageVersions:
   linux-restricted-modules-3.11.0-15-generic N/A
   linux-backports-modules-3.11.0-15-generic  N/A
   linux-firmware                             1.116.1
  SourcePackage: linux
  UpgradeStatus: Upgraded to saucy on 2013-11-13 (91 days ago)
  dmi.bios.date: 10/31/2011
  dmi.bios.vendor: LENOVO
  dmi.bios.version: 83ET66WW (1.36 )
  dmi.board.asset.tag: Not Available
  dmi.board.name: 4180W1G
  dmi.board.vendor: LENOVO
  dmi.board.version: Not Available
  dmi.chassis.asset.tag: No Asset Information
  dmi.chassis.type: 10
  dmi.chassis.vendor: LENOVO
  dmi.chassis.version: Not Available
  dmi.modalias: dmi:bvnLENOVO:bvr83ET66WW(1.36):bd10/31/2011:svnLENOVO:pn4180W1G:pvrThinkPadT420:rvnLENOVO:rn4180W1G:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable:
  dmi.product.name: 4180W1G
  dmi.product.version: ThinkPad T420
  dmi.sys.vendor: LENOVO

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