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[Andrey Makeev <amaksoft@xxxxxxxxx>]

Testing with 4.5-rc1 results:
/sys/class/backlight/acpi_video0/ appeared.
Brightness changes if i echo the value to /sys/class/backlight/acpi_video0/brightness

Tracked it down to this kernel.org bug report:
https://bugzilla.kernel.org/show_bug.cgi?id=108971
It seems to be exactly the same issue.

For now I added kernel parameter acpi_backlight=video to grub config and
changed backlight control interface in xorg.conf  to acpi_video0. Works
fine.

** Bug watch added: Linux Kernel Bug Tracker #108971
   http://bugzilla.kernel.org/show_bug.cgi?id=108971

** Changed in: linux (Ubuntu)
       Status: Incomplete => Confirmed

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https://bugs.launchpad.net/bugs/1537324

Title:
  No brightness control on Samsung NP530U4E-K01RU

Status in linux package in Ubuntu:
  Confirmed

Bug description:
  Backlight control does not work, but there are entries in
  /sys/class/backlight.

  Laptop model: NP530U4E-K01RU
  Video adapter: Intel HD graphics 4000

  I've tried all the suggestions from
  https://wiki.ubuntu.com/Kernel/Debugging/Backlight

  kernel parameters  acpi_backlight=vendor,
  video.use_bios_initial_backlight=0,  video.use_native_backlight=1
  didn't work.

  In this laptop brightness is controlled by Fn+F2 and Fn+F3. Whenever i
  try to change brightness, the value in
  /sys/class/backlight/intel_backlight/brightness and
  /sys/class/backlight/intel_backlight/actual_brightness changes, but
  actual screen brightness is the same:

  $ grep . /sys/class/backlight/intel_backlight/*
  /sys/class/backlight/intel_backlight/actual_brightness:2792
  /sys/class/backlight/intel_backlight/bl_power:0
  /sys/class/backlight/intel_backlight/brightness:2792
  grep: /sys/class/backlight/intel_backlight/device: Is a directory
  /sys/class/backlight/intel_backlight/max_brightness:4648
  grep: /sys/class/backlight/intel_backlight/power: Is a directory
  grep: /sys/class/backlight/intel_backlight/subsystem: Is a directory
  /sys/class/backlight/intel_backlight/type:raw

  All the logs are in the attached archive backlight_bug_report.tar.gz

  ProblemType: Bug
  DistroRelease: Ubuntu 15.10
  Package: linux-image-4.2.0-25-generic 4.2.0-25.30
  ProcVersionSignature: Ubuntu 4.2.0-25.30-generic 4.2.6
  Uname: Linux 4.2.0-25-generic x86_64
  ApportVersion: 2.19.1-0ubuntu5
  Architecture: amd64
  CurrentDesktop: Unity
  Date: Sat Jan 23 09:55:32 2016
  HibernationDevice: RESUME=UUID=9d4a6619-c5f9-46c2-b11b-e230e9d357e3
  InstallationDate: Installed on 2014-05-20 (613 days ago)
  InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1)
  MachineType: SAMSUNG ELECTRONICS CO., LTD. 530U4E/540U4E
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.2.0-25-generic root=UUID=686fa320-83d1-4015-a632-bb2a91390ab6 ro quiet splash video.use_bios_initial_backlight=0 vt.handoff=7
  RelatedPackageVersions:
   linux-restricted-modules-4.2.0-25-generic N/A
   linux-backports-modules-4.2.0-25-generic  N/A
   linux-firmware                            1.149.3
  SourcePackage: linux
  UpgradeStatus: Upgraded to wily on 2015-11-25 (58 days ago)
  dmi.bios.date: 02/26/2014
  dmi.bios.vendor: American Megatrends Inc.
  dmi.bios.version: P08ACM.065.140226.dg
  dmi.board.asset.tag: No Asset Tag
  dmi.board.name: NP530U4E-K01RU
  dmi.board.vendor: SAMSUNG ELECTRONICS CO., LTD.
  dmi.board.version: SEC_SW_REVISION_1234567890ABCD
  dmi.chassis.asset.tag: No Asset Tag
  dmi.chassis.type: 9
  dmi.chassis.vendor: SAMSUNG ELECTRONICS CO., LTD.
  dmi.chassis.version: N/A
  dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrP08ACM.065.140226.dg:bd02/26/2014:svnSAMSUNGELECTRONICSCO.,LTD.:pn530U4E/540U4E:pvrP08ACM:rvnSAMSUNGELECTRONICSCO.,LTD.:rnNP530U4E-K01RU:rvrSEC_SW_REVISION_1234567890ABCD:cvnSAMSUNGELECTRONICSCO.,LTD.:ct9:cvrN/A:
  dmi.product.name: 530U4E/540U4E
  dmi.product.version: P08ACM
  dmi.sys.vendor: SAMSUNG ELECTRONICS CO., LTD.

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