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[Po-Hsu Lin <po-hsu.lin@xxxxxxxxxxxxx>]

There's one ACPI related bug on 3.8 kernel, bug 1249978

According to Keng-Yu, this bug is related to brightness control through
ACPI

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https://bugs.launchpad.net/bugs/1250764

Title:
  [Dell Latitude E6440] Unable to adjust brightness on Precise

Status in “linux” package in Ubuntu:
  Confirmed

Bug description:
  CID: 201306-13688 Dell Latitude E6440

  Backlight control does not work on Precise (3.2.0-56):
  1. Hotkey event was not detected.
  2. No scroll bar in brightness applet.
  3. No entries in /sys/class/backlight. 

  Steps:
  1. Install 12.04.1 + update
  2. Try to adjust the brightness by hotkeys
  3. Try to adjust the brightness by the brightness applet

  Expected result:
  Brightness could be adjusted.

  Actual result:
  Hotkeys are not responding, no scroll bar in brightness applet.

  Debugging information:
  $ ls /sys/class/backlight > backlight 
  (Nothing)

  $ dmesg | grep 'ACPI: Video'
  (Nothing)

  $ cat /proc/version
  Linux version 3.2.0-56-generic (buildd@roseapple) (gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) ) #86-Ubuntu SMP Wed Oct 23 09:20:45 UTC 2013

  Boot with "acpi_backlight=vendor" kernel parameter
  The hotkey could change the indicator level, and the scroll bar would appear in brightness applet.
  However, the brightness still cannot be altered.

  $ ls /sys/class/backlight/
  dell_backlight

  Boot with "video.use_bios_initial_backlight=0" kernel parameter
  It behaves like without adding any other parameter.

  ProblemType: Bug
  DistroRelease: Ubuntu 12.04
  Package: linux-image-3.2.0-56-generic 3.2.0-56.86
  ProcVersionSignature: Ubuntu 3.2.0-56.86-generic 3.2.51
  Uname: Linux 3.2.0-56-generic x86_64
  AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.24.
  AplayDevices:
   **** List of PLAYBACK Hardware Devices ****
   card 1: PCH [HDA Intel PCH], device 0: ALC292 Analog [ALC292 Analog]
     Subdevices: 1/1
     Subdevice #0: subdevice #0
  ApportVersion: 2.0.1-0ubuntu17.6
  Architecture: amd64
  ArecordDevices:
   **** List of CAPTURE Hardware Devices ****
   card 1: PCH [HDA Intel PCH], device 0: ALC292 Analog [ALC292 Analog]
     Subdevices: 1/1
     Subdevice #0: subdevice #0
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC1:  ubuntu     1566 F.... pulseaudio
  Card0.Amixer.info:
   Card hw:0 'Intel'/'HDA Intel at 0xf7d34000 irq 43'
     Mixer name	: 'Generic 0000 ID 0'
     Components	: 'HDA:00000000,80860101,00100000'
     Controls      : 0
     Simple ctrls  : 0
  Card0.Amixer.values:
   
  Card1.Amixer.info:
   Card hw:1 'PCH'/'HDA Intel PCH at 0xf7d30000 irq 43'
     Mixer name	: 'Realtek ALC292'
     Components	: 'HDA:10ec0292,102805bd,00100001'
     Controls      : 19
     Simple ctrls  : 10
  Date: Wed Nov 13 03:16:25 2013
  HibernationDevice: RESUME=UUID=aeb30de4-c85d-4d93-874d-8f06ce1303b2
  InstallationMedia: Ubuntu 12.04.1 LTS "Precise Pangolin" - Release amd64 (20120823.1)
  MachineType: Dell Inc. Latitude E6440
  MarkForUpload: True
  ProcEnviron:
   TERM=xterm
   PATH=(custom, no user)
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  ProcFB: 0 VESA VGA
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.2.0-56-generic root=UUID=3cde48ea-3225-4afa-b02b-584a672a94e4 ro quiet splash vt.handoff=7
  RelatedPackageVersions:
   linux-restricted-modules-3.2.0-56-generic N/A
   linux-backports-modules-3.2.0-56-generic  N/A
   linux-firmware                            1.79.7
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 07/03/2013
  dmi.bios.vendor: Dell Inc.
  dmi.bios.version: X23
  dmi.board.name: 02P3T1
  dmi.board.vendor: Dell Inc.
  dmi.board.version: X03
  dmi.chassis.type: 9
  dmi.chassis.vendor: Dell Inc.
  dmi.modalias: dmi:bvnDellInc.:bvrX23:bd07/03/2013:svnDellInc.:pnLatitudeE6440:pvr01:rvnDellInc.:rn02P3T1:rvrX03:cvnDellInc.:ct9:cvr:
  dmi.product.name: Latitude E6440
  dmi.product.version: 01
  dmi.sys.vendor: Dell Inc.

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