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[Anthony Wong <anthony.wong@xxxxxxxxxx>]

@Joseph
To workaround, append acpi_backlight=vendor on line GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub, then run 'sudo update-grub'.

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https://bugs.launchpad.net/bugs/1393644

Title:
  [Dell Inspiron 3531] Brightness control does not work on 14.04.1

Status in HWE Next Project:
  Triaged
Status in linux package in Ubuntu:
  Confirmed

Bug description:
  CID: 201403-14892  Inspiron 3531

  Brightness control does not work on this system
  The brightness level indicator would change with hotkey events, but the brightness itself does not.

  Debugging information:
  ubuntu@201403-14892:~$ ls /sys/class/backlight
  acpi_video0  intel_backlight

  ubuntu@201403-14892:~$ grep -r . /proc/acpi
  /proc/acpi/battery/BAT1/alarm:alarm:                   unsupported
  /proc/acpi/battery/BAT1/state:present:                 yes
  /proc/acpi/battery/BAT1/state:capacity state:          ok
  /proc/acpi/battery/BAT1/state:charging state:          charged
  /proc/acpi/battery/BAT1/state:present rate:            1 mA
  /proc/acpi/battery/BAT1/state:remaining capacity:      2508 mAh
  /proc/acpi/battery/BAT1/state:present voltage:         17028 mV
  /proc/acpi/battery/BAT1/info:present:                 yes
  /proc/acpi/battery/BAT1/info:design capacity:         2800 mAh
  /proc/acpi/battery/BAT1/info:last full capacity:      2508 mAh
  /proc/acpi/battery/BAT1/info:battery technology:      rechargeable
  /proc/acpi/battery/BAT1/info:design voltage:          14800 mV
  /proc/acpi/battery/BAT1/info:design capacity warning: 250 mAh
  /proc/acpi/battery/BAT1/info:design capacity low:     75 mAh
  /proc/acpi/battery/BAT1/info:cycle count:		  0
  /proc/acpi/battery/BAT1/info:capacity granularity 1:  264 mAh
  /proc/acpi/battery/BAT1/info:capacity granularity 2:  3780 mAh
  /proc/acpi/battery/BAT1/info:model number:            DELL T1G4M2CK
  /proc/acpi/battery/BAT1/info:serial number:           0E4C
  /proc/acpi/battery/BAT1/info:battery type:            Li-Ion
  /proc/acpi/battery/BAT1/info:OEM info:                LGC
  /proc/acpi/button/lid/LID0/state:state:      open
  /proc/acpi/ac_adapter/ACAD/state:state:                   on-line
  /proc/acpi/wakeup:Device	S-state	  Status   Sysfs node
  /proc/acpi/wakeup:LID0	  S3	*enabled 
  /proc/acpi/wakeup:RP01	  S4	*disabled  pci:0000:00:1c.0
  /proc/acpi/wakeup:PXSX	  S4	*disabled
  /proc/acpi/wakeup:RP02	  S4	*disabled  pci:0000:00:1c.1
  /proc/acpi/wakeup:PXSX	  S4	*disabled  pci:0000:02:00.0
  /proc/acpi/wakeup:RP03	  S4	*disabled  pci:0000:00:1c.2
  /proc/acpi/wakeup:PXSX	  S4	*disabled
  /proc/acpi/wakeup:RP04	  S4	*disabled  pci:0000:00:1c.3
  /proc/acpi/wakeup:PXSX	  S4	*disabled
  /proc/acpi/wakeup:EHC1	  S0	*enabled   pci:0000:00:1d.0
  /proc/acpi/wakeup:PWRB	  S4	*enabled 

  ubuntu@201403-14892:~$ dmesg | grep 'ACPI: Video'
  [   17.318290] ACPI: Video Device [GFX0] (multi-head: yes  rom: no  post: no)
  ubuntu@201403-14892:~$

  WORKAROUND:
  Adding "acpi_backlight=vendor" to grub could make it work.

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: linux-image-3.13.0-39-generic 3.13.0-39.66
  ProcVersionSignature: Ubuntu 3.13.0-39.66-generic 3.13.11.8
  Uname: Linux 3.13.0-39-generic x86_64
  ApportVersion: 2.14.1-0ubuntu3.5
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC0:  ubuntu     1520 F.... pulseaudio
  CRDA:
   country TW:
   	(2402 - 2472 @ 40), (3, 27)
   	(5270 - 5330 @ 40), (3, 17), DFS
   	(5735 - 5815 @ 40), (3, 30)
  CurrentDesktop: Unity
  Date: Mon Nov 17 21:37:21 2014
  HibernationDevice: RESUME=UUID=217ae5ce-6101-4b1d-8ed3-e5df8cacfafa
  InstallationDate: Installed on 2014-11-17 (0 days ago)
  InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
  Lsusb:
   Bus 001 Device 005: ID 0bda:0129 Realtek Semiconductor Corp. RTS5129 Card Reader Controller
   Bus 001 Device 004: ID 1a40:0101 Terminus Technology Inc. Hub
   Bus 001 Device 003: ID 0c45:64ad Microdia 
   Bus 001 Device 002: ID 8087:07e6 Intel Corp. 
   Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
  MachineType: Dell Inc. Inspiron 3531
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-39-generic root=UUID=34aa7766-e502-48af-81d4-5a155b69c395 ro quiet splash vt.handoff=7
  RelatedPackageVersions:
   linux-restricted-modules-3.13.0-39-generic N/A
   linux-backports-modules-3.13.0-39-generic  N/A
   linux-firmware                             1.127.8
  RfKill:
   0: phy0: Wireless LAN
   	Soft blocked: no
   	Hard blocked: no
  SourcePackage: linux
  StagingDrivers: rts5139
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 07/02/2014
  dmi.bios.vendor: Dell Inc.
  dmi.bios.version: A02_UpdateMCU
  dmi.board.name: 00FTTX
  dmi.board.vendor: Dell Inc.
  dmi.board.version: A00
  dmi.chassis.type: 8
  dmi.chassis.vendor: Dell Inc.
  dmi.chassis.version: A02_UpdateMCU
  dmi.modalias: dmi:bvnDellInc.:bvrA02_UpdateMCU:bd07/02/2014:svnDellInc.:pnInspiron3531:pvrA02_UpdateMCU:rvnDellInc.:rn00FTTX:rvrA00:cvnDellInc.:ct8:cvrA02_UpdateMCU:
  dmi.product.name: Inspiron 3531
  dmi.product.version: A02_UpdateMCU
  dmi.sys.vendor: Dell Inc.

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