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[RavanH <1309462@xxxxxxxxxxxxxxxxxx>]

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

Title:
  Intel Ivybridge Mobile graphics backlight not adjustable

Status in “linux” package in Ubuntu:
  Confirmed

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 (this will
  change after testing with kernel parameters!) 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 / Yes *

  > 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.

  No / Yes *

  > If your backlight hotkeys are Fn+Left and Fn+Right, add kernel
  parameter atkbd.softraw=0 to /boot/grub/menu.lst

  They are so I did (not /boot/grub/menu.lst but /etc/default/grub
  though...) and I rebooted even though it is not written I should...

  > Then, switch to any console, e.g. Ctrl+Alt+F1, login by root account
  and execute: showkey -s

  I did (after reboot mentioned above) and found that the hotkeys do not
  give any output at all anymore... Strange. So I reverted all changed
  above and rebooted with only "quiet splash" boot parameters but still
  the hotkeys remain dead. Not even the faux brightness slider change
  anymore. Very strange!

  * 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
  intel_backlight

  Note that this used to list video0_backlight (as I remember it) too
  but after testing and reverting (!) that entry remains gone. Strange.

  $ 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 acpi_backlight=vendor 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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