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[Tobias Eichert <mail@xxxxxxxxxx>]

For my Thinkpad T430s, I can confirm that adding acpi_backlight=vendor
as a grub boot option fixes the problem. I only have the Intel GPU
enabled.

However, applying this boot options result in the OSD not correctly
showing the current brightness state (s. attachment); it has always the
same state.

** Attachment added: "Screenshot from 2013-09-27 01:44:43.png"
   https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1221795/+attachment/3843507/+files/Screenshot%20from%202013-09-27%2001%3A44%3A43.png

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https://bugs.launchpad.net/bugs/1221795

Title:
  brightness stepping is incorrect (double what it should be)

Status in “linux” package in Ubuntu:
  Incomplete

Bug description:
  Problem:  When I press the laptop screen brighteness, each step yield
  an event that is displayed on the OSD but the screen brightness
  doesn't change until the third press. Same happens for decreasing or
  increasing the brightness.

  Exepcted behaviour: Each press of the brightness button on the laptop,
  yield a visible change in the brightness of the LCD scree.

  Workaround: This seems documented and works perfectly. The work around
  is to type this in terminal:

  sudo sh -c 'echo -n 0 >
  /sys/module/video/parameters/brightness_switch_enabled'

  More details are here: http://askubuntu.com/questions/173921/why-does-
  my-thinkpad-brightness-control-skip-steps

  I think this should be fixed in 13.10.

  ProblemType: Bug
  DistroRelease: Ubuntu 13.10
  Package: linux-image-3.11.0-4-generic 3.11.0-4.9
  ProcVersionSignature: Ubuntu 3.11.0-4.9-generic 3.11.0-rc7
  Uname: Linux 3.11.0-4-generic x86_64
  ApportVersion: 2.12.1-0ubuntu3
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC0:  anmar      1798 F.... pulseaudio
  Date: Fri Sep  6 11:23:20 2013
  HibernationDevice: RESUME=UUID=2e39ee55-2a87-4298-a2d0-1c8ef5de5a96
  InstallationDate: Installed on 2013-08-09 (27 days ago)
  InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Alpha amd64 (20130809)
  MachineType: LENOVO 3443CTO
  MarkForUpload: True
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.11.0-4-generic.efi.signed root=UUID=1784df7c-8b5f-4550-84f2-13e73c2915fe ro quiet splash vt.handoff=7
  RelatedPackageVersions:
   linux-restricted-modules-3.11.0-4-generic N/A
   linux-backports-modules-3.11.0-4-generic  N/A
   linux-firmware                            1.113
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 04/29/2013
  dmi.bios.vendor: LENOVO
  dmi.bios.version: G6ET96WW (2.56 )
  dmi.board.asset.tag: Not Available
  dmi.board.name: 3443CTO
  dmi.board.vendor: LENOVO
  dmi.board.version: Win8 STD DPK TPG
  dmi.chassis.asset.tag: No Asset Information
  dmi.chassis.type: 10
  dmi.chassis.vendor: LENOVO
  dmi.chassis.version: Not Available
  dmi.modalias: dmi:bvnLENOVO:bvrG6ET96WW(2.56):bd04/29/2013:svnLENOVO:pn3443CTO:pvrThinkPadX1Carbon:rvnLENOVO:rn3443CTO:rvrWin8STDDPKTPG:cvnLENOVO:ct10:cvrNotAvailable:
  dmi.product.name: 3443CTO
  dmi.product.version: ThinkPad X1 Carbon
  dmi.sys.vendor: LENOVO

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