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["Christopher M. Penalver" <christopher.m.penalver@xxxxxxxxx>]

Siddharth Agarwal, thank you for your comment. So your hardware and problem may be tracked, could you please file a new report with Ubuntu by executing the following in a terminal while booted into a Ubuntu repository kernel (not a mainline one) via:
ubuntu-bug linux

For more on this, please read the official Ubuntu documentation:
Ubuntu Bug Control and Ubuntu Bug Squad: https://wiki.ubuntu.com/Bugs/BestPractices#X.2BAC8-Reporting.Focus_on_One_Issue
Ubuntu Kernel Team: https://wiki.ubuntu.com/KernelTeam/KernelTeamBugPolicies#Filing_Kernel_Bug_reports
Ubuntu Community: https://help.ubuntu.com/community/ReportingBugs#Bug_reporting_etiquette

When opening up the new report, please feel free to subscribe me to it.

Thank you for your understanding.

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

** Changed in: linux (Ubuntu)
       Status: Confirmed => Incomplete

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https://bugs.launchpad.net/bugs/1308674

Title:
  [Lenovo ThinkPad X220] kernel 3.13 i915 brightness settings broken
  when going from docked -> undocked

Status in The Linux Kernel:
  New
Status in “linux” package in Ubuntu:
  Incomplete
Status in “linux” package in Fedora:
  Unknown

Bug description:
  This happens on my X220, running trusty, linux 3.13.0-24-generic. It's
  the exact same problem discussed on
  https://bugzilla.redhat.com/show_bug.cgi?id=1067071. Discussed also on
  kernel mailing list: https://lkml.org/lkml/2014/2/19/720. It worked on
  3.12, and upstream acknowledges the regression.

  To reproduce, remove the X220 from the dock. The brightness is set to
  minimum (the screen is nearly unreadable) and the brightness control
  is broken, you can't adjust it by hardware keys.

  My hardware:
  00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09) (prog-if 00 [VGA controller])
   Subsystem: Lenovo Device 21da
   Kernel driver in use: i915
  Docked on a ThinkPad mini dock series 3.

  I have nothing much relevant in /var/log/syslog. Below there are
  excerpts of it when brightness is working:

  Apr 16 14:55:37 galactica kernel: [79261.217384] [drm:asle_set_backlight], bclp = 0x800000ff
  Apr 16 14:55:37 galactica kernel: [79261.217390] [drm:asle_set_backlight], updating opregion backlight 255/255
  Apr 16 14:55:37 galactica kernel: [79261.217394] [drm:intel_panel_get_max_backlight], max backlight PWM = 4648
  Apr 16 14:55:37 galactica kernel: [79261.217396] [drm:intel_panel_actually_set_backlight], set backlight PWM = 4590
  Apr 16 14:55:37 galactica kernel: [79261.217537] [drm:asle_set_pwm_freq], PWM freq is not supported

  And brightness not working:

  Apr 16 15:23:46 galactica kernel: [80948.263160] [drm:asle_set_backlight], bclp = 0x80000058
  Apr 16 15:23:46 galactica kernel: [80948.263168] [drm:asle_set_pwm_freq], PWM freq is not supported
  Apr 16 15:23:46 galactica kernel: [80948.280637] [drm:asle_set_backlight], bclp = 0x80000041
  Apr 16 15:23:46 galactica kernel: [80948.280642] [drm:asle_set_pwm_freq], PWM freq is not supported

  A workaround is to echo values directly to /sys/class/backlight/intel_backlight/brightness. Maximum brightness is 4648 (/sys/class/backlight/intel_backlight/max_brightness).
  e.g.: # echo 500 > /sys/class/backlight/intel_backlight/brightness

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: linux-image-3.13.0-24-generic 3.13.0-24.46
  ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
  Uname: Linux 3.13.0-24-generic i686
  ApportVersion: 2.14.1-0ubuntu2
  Architecture: i386
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC1:  ursula     3881 F.... pulseaudio
   /dev/snd/controlC0:  ursula     3881 F.... pulseaudio
  CurrentDesktop: Unity
  Date: Wed Apr 16 15:09:23 2014
  HibernationDevice: RESUME=UUID=68890e28-0eee-4184-9456-cc267c4a5f31
  InstallationDate: Installed on 2013-05-27 (323 days ago)
  InstallationMedia: Ubuntu 12.04.2 LTS "Precise Pangolin" - Release i386 (20130213)
  MachineType: LENOVO 4286CTO
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-24-generic root=UUID=4db5451d-c250-47bc-9c4e-235fb1967ee5 ro quiet splash vt.handoff=7
  RelatedPackageVersions:
   linux-restricted-modules-3.13.0-24-generic N/A
   linux-backports-modules-3.13.0-24-generic  N/A
   linux-firmware                             1.127
  SourcePackage: linux
  UpgradeStatus: Upgraded to trusty on 2013-11-04 (162 days ago)
  dmi.bios.date: 12/01/2011
  dmi.bios.vendor: LENOVO
  dmi.bios.version: 8DET56WW (1.26 )
  dmi.board.asset.tag: Not Available
  dmi.board.name: 4286CTO
  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:bvr8DET56WW(1.26):bd12/01/2011:svnLENOVO:pn4286CTO:pvrThinkPadX220:rvnLENOVO:rn4286CTO:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable:
  dmi.product.name: 4286CTO
  dmi.product.version: ThinkPad X220
  dmi.sys.vendor: LENOVO

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