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[RavanH <1309462@xxxxxxxxxxxxxxxxxx>]

** Tags removed: kernel-bug-exists-upstream-1.13.10 kernel-bug-exists-upstream-1.14.1
** Tags added: kernel-bug-exists-upstream-3.13.10 kernel-bug-exists-upstream-3.14.1

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https://bugs.launchpad.net/bugs/1309462

Title:
  8086:0166 [Aspire V5-571P] Backlight not adjustable

Status in “linux” package in Ubuntu:
  Incomplete

Bug description:
  On an Acer Aspire V5 with Intel Graphics, backlight control is not
  working. Both on Ubuntu GNOME 13.10 and 14.04 neither hotkeys or
  adjusting the applet slider has any effect. Note that the hotkeys
  Fn+Left and Fn+Right DO result in a moving slider indicator but no
  actual backlight change.

  Following https://wiki.ubuntu.com/Kernel/Debugging/Backlight "Testing
  for a workaround"  here are my findings. More debugging info will be
  attached later.

  TESTING FOR A WORK AROUND

  > Reboot with only the kernel parameter acpi_backlight=vendor :
  > Make a comment on if you can now alter the backlight with hotkeys or a brightness applet.

  No / Yes *

  > sudo su
  > echo 8 > /sys/class/backlight/intel_backlight/brightness
  > Please comment on if the brightness changes.

  Yes

  > Reboot with just kernel parameter video.use_bios_initial_backlight=0
  > and make a comment on if you can now alter the backlight with hotkeys or a brightness applet.

  No / No

  > If using a v3.13.x+ series kernel, reboot with just kernel parameter video.use_native_backlight=1
  > and make a comment on if you can now alter the backlight with hotkeys or a brightness applet.

  Yes / Yes *

  * please note that there is no brightness applet in Ubuntu GNOME 14.04
  but going to the Settings > Screen Brightness & Lock the brightness
  can now be controlled

  BASIC DEBUGGING INFORMATION (all files will be attached later)

  $ ls /sys/class/backlight
  acpi_video0 intel_backlight

  $ dmesg | grep 'ACPI: Video'
  [    2.969975] ACPI: Video Device [GFX0] (multi-head: yes  rom: no  post: no)

  $ lspci | grep VGA
  00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09)

  $ cat /proc/version
  Linux version 3.13.0-24-generic (buildd@panlong) (gcc version 4.8.2 (Ubuntu 4.8.2-19ubuntu1) ) #46-Ubuntu SMP Thu Apr 10 19:11:08 UTC 2014

  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 x86_64
  ApportVersion: 2.14.1-0ubuntu3
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC0:  ravanhagen   1918 F.... pulseaudio
  CurrentDesktop: GNOME
  Date: Fri Apr 18 12:03:12 2014
  EcryptfsInUse: Yes
  InstallationDate: Installed on 2014-04-14 (3 days ago)
  InstallationMedia: Ubuntu-GNOME 14.04 LTS "Trusty Tahr" - Daily amd64 (20140406)
  MachineType: Acer Aspire V5-571P
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-24-generic.efi.signed root=UUID=631fc653-5697-44cb-b877-f6cae0fda9cf 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: No upgrade log present (probably fresh install)
  dmi.bios.date: 11/16/2012
  dmi.bios.vendor: Phoenix Technologies Ltd.
  dmi.bios.version: V2.13
  dmi.board.asset.tag: No Asset Tag
  dmi.board.name: Aspire V5-571P
  dmi.board.vendor: Acer
  dmi.board.version: V2.13
  dmi.chassis.asset.tag: No Asset Tag
  dmi.chassis.type: 9
  dmi.chassis.vendor: Acer
  dmi.chassis.version: V2.13
  dmi.modalias: dmi:bvnPhoenixTechnologiesLtd.:bvrV2.13:bd11/16/2012:svnAcer:pnAspireV5-571P:pvrV2.13:rvnAcer:rnAspireV5-571P:rvrV2.13:cvnAcer:ct9:cvrV2.13:
  dmi.product.name: Aspire V5-571P
  dmi.product.version: V2.13
  dmi.sys.vendor: Acer

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