No brightness control on Samsung NP530U4E-K01RU

[Andrey Makeev]

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.

[Brad Figg (brad-figg)]

This change was made by a bot.

[Joseph Salisbury (jsalisbury)]

Would it be possible for you to test the latest upstream kernel? Refer to https://wiki.ubuntu.com/KernelMainlineBuilds . Please test the latest v4.4 kernel[0].

If this bug is fixed in the mainline kernel, please add the following tag 'kernel-fixed-upstream'.

If the mainline kernel does not fix this bug, please add the tag: 'kernel-bug-exists-upstream'.

Once testing of the upstream kernel is complete, please mark this bug as "Confirmed".

Thanks in advance.

[0] http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.4-wily

[Andrey Makeev (amaksoft)]

I've tested it on v4.4-wily and v4.4-rc8-wily. Same problem: /sys/class/backlight/intel_backlight/brightness changes, but the actual screen brightness doesn't.

[penalvch (penalvch)]

Andrey Makeev, the latest mainline kernel (4.5-rc1) was released two days ago. Could you please test this and advise to the results?

[Andrey Makeev (amaksoft)]

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.