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[jalon <jalonwong@xxxxxxxxx>]

I have the same issue in Ubuntu 12.04.3. My laptop is Dell Latitude
3540.

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https://bugs.launchpad.net/bugs/1069357

Title:
  [Dell Vostro V131] Hardware keys change backlight brightness in much
  larger increments/steps than expected

Status in “linux” package in Ubuntu:
  Incomplete

Bug description:
  SInce the upgrade to Ubuntu 12.10,  hardware keys for regulating
  backlight brightness (fn+f4, fn+f5) change brightness in large
  increments, even though much finer control is available both through
  the Brightness and Lock dialog in Settings and by just setting the
  value in /sys/class/backlight/acpi_video0/brightness, for example:

  # echo 1 > /sys/class/backlight/acpi_video0/brightness

  /sys/class/backlight/acpi_video0/brightness accepts values 0-15, the
  default step seems to be 3 instead of 1 as expected, and as it was in
  Ubuntu 12.04.

  Partial workaround is to disable brightness switch

  # echo -n 0 > /sys/module/video/parameters/brightness_switch_enabled

  which cuts the step to 2. Moreover, adding kernel parameters
  "acpi_osi=Linux acpi_backlight=legacy" allows for even finer control
  in the Brightness and Lock dialog in Settings (finer than those 16
  settings, including completely turning the backlight via the
  brightness slider) but breaks the hardware keys functionality
  completely.

  # lsb_release -rd
  Description:	Ubuntu 12.10
  Release:	12.10
  --- 
  ApportVersion: 2.6.1-0ubuntu3
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC0:  rmo        1897 F.... pulseaudio
  DistroRelease: Ubuntu 12.10
  HibernationDevice: RESUME=UUID=7c82e11d-4211-4789-90b6-7a20abd8aa82
  InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Release amd64 (20121017.5)
  MachineType: Dell Inc. Vostro V131
  Package: linux (not installed)
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.5.0-17-generic root=/dev/mapper/ubuntu-root ro
  ProcVersionSignature: Ubuntu 3.5.0-17.28-generic 3.5.5
  RelatedPackageVersions:
   linux-restricted-modules-3.5.0-17-generic N/A
   linux-backports-modules-3.5.0-17-generic  N/A
   linux-firmware                            1.95
  Tags:  quantal running-unity
  Uname: Linux 3.5.0-17-generic x86_64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
  dmi.bios.date: 10/24/2011
  dmi.bios.vendor: Dell Inc.
  dmi.bios.version: A03
  dmi.board.name: 0X3GJK
  dmi.board.vendor: Dell Inc.
  dmi.board.version: A03
  dmi.chassis.type: 8
  dmi.chassis.vendor: Dell Inc.
  dmi.chassis.version: Not Specified
  dmi.modalias: dmi:bvnDellInc.:bvrA03:bd10/24/2011:svnDellInc.:pnVostroV131:pvrNotSpecified:rvnDellInc.:rn0X3GJK:rvrA03:cvnDellInc.:ct8:cvrNotSpecified:
  dmi.product.name: Vostro V131
  dmi.product.version: Not Specified
  dmi.sys.vendor: Dell Inc.

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