Samsung 730U3E LCD backlight brightness control doesn't work

[Stefan Burnicki]

Fn-shortcuts work and the value in /sys/class/backlight/intel_backlight/brightness changes, but is has no physical effect.
Only setting /sys/class/backlight/intel_backlight/brightness to 0 turns the LCD off, changing it to any other value turns it on again.

I tried to set different boot parameters in /etc/defaults/grub
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video.use_native_backlight=1"
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video.use_native_backlight=0"
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi=Linux acpi_backlight=vendor"
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video.use_bios_initial_backlight=0"

For each change, I called update-grub, restarted, and verfied the settings with /proc/cmdline. Nothing worked for me.

I also tested this with the newest mainline kernel (4.1-rc2), but the bug still exists.

It work with trusty and stopped working with utopic. I thought this issue would may be fixed in vivid, but it isn't.

Please tell me what other information you need in order to fix this.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: linux-image-3.19.0-16-generic 3.19.0-16.16
ProcVersionSignature: Ubuntu 3.19.0-16.16-generic 3.19.3
Uname: Linux 3.19.0-16-generic x86_64
ApportVersion: 2.17.2-0ubuntu1
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: stefan 1383 F.... pulseaudio
CurrentDesktop: KDE
Date: Tue May 12 13:08:51 2015
HibernationDevice: RESUME=UUID=34e06653-f31c-45ef-80ca-9eddcae5134f
InstallationDate: Installed on 2015-03-10 (62 days ago)
InstallationMedia: Kubuntu-Plasma-5 14.10 "Utopic Unicorn" - Release amd64 (20141022)
MachineType: SAMSUNG ELECTRONICS CO., LTD. 730U3E/740U3E
ProcFB:
 0 inteldrmfb
 1 radeondrmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.19.0-16-generic root=/dev/mapper/kubuntu--plasma--5--vg-root ro quiet splash video.use_bios_initial_backlight=0
RelatedPackageVersions:
 linux-restricted-modules-3.19.0-16-generic N/A
 linux-backports-modules-3.19.0-16-generic N/A
 linux-firmware 1.143
SourcePackage: linux
UpgradeStatus: Upgraded to vivid on 2015-04-26 (16 days ago)
dmi.bios.date: 05/30/2013
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: P05ABW.060.130530.dg
dmi.board.asset.tag: No Asset Tag
dmi.board.name: NP730U3E-S03DE
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.:bvrP05ABW.060.130530.dg:bd05/30/2013:svnSAMSUNGELECTRONICSCO.,LTD.:pn730U3E/740U3E:pvrP05ABW:rvnSAMSUNGELECTRONICSCO.,LTD.:rnNP730U3E-S03DE:rvrSEC_SW_REVISION_1234567890ABCD:cvnSAMSUNGELECTRONICSCO.,LTD.:ct9:cvrN/A:
dmi.product.name: 730U3E/740U3E
dmi.product.version: P05ABW
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 v4.1 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'.

If you are unable to test the mainline kernel, for example it will not boot, please add the tag: 'kernel-unable-to-test-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/v4.1-rc3-vivid/

[Stefan Burnicki (stefan-burnicki)]

Just tested it with 4.1 rc3 but the problem remains the same.

[Stefan Burnicki (stefan-burnicki)]

Okay, my upstream kernel test was a little naive.

When I was bisecting the problem, I noticed that my test to control the brightness failed even with kernels that worked before.
So I noticed that I still had a /usr/share/X11/xorg.conf.d/80-intel.conf file with:
Section "Device"
    Identifier "card0"
    Driver "intel"
    Option "AccelMethod" "sna"
    Option "Backlight" "intel_backlight" # use your backlight that works here
    BusID "PCI:0:2:0"
EndSection

After *removing* that file, it worked for me in the old kernel versions, so I tried the upstream kernel again and it works. So it's fixed in an upstream kernel, which is fine for me, as it seems to be pretty stable.

[penalvch (penalvch)]

Stefan Burnicki, just to clarify, when you removed the modification, does the default Ubuntu kernel still not work?

[Stefan Burnicki (stefan-burnicki)]

The default ubuntu kernel (currently 3.19.0-16) does not work for me.
In /sys/class/backlight there is only

intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight

However, with 4.1-rc3 there is

acpi_video0 -> ../../devices/pci0000:00/0000:00:01.0/0000:01:00.0/backlight/acpi_video0
acpi_video1 -> ../../devices/pci0000:00/0000:00:02.0/backlight/acpi_video1
intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight

The first one can be used to control my LCD backlight.

[penalvch (penalvch)]

Stefan Burnicki, the next step is to fully reverse commit bisect from kernel 4.1-rc2 to 4.1-rc3 in order to identify the last bad commit, followed immediately by the first good one. Once this commit has been identified, then it may be reviewed as a candidate for backporting into your release. Could you please do this following https://wiki.ubuntu.com/Kernel/KernelBisection#How_do_I_reverse_bisect_the_upstream_kernel.3F ?

Please note, finding adjacent kernel versions is not fully commit bisecting.

Thank you for your understanding.

Helpful bug reporting tips:
https://wiki.ubuntu.com/ReportingBugs

[Stefan Burnicki (stefan-burnicki)]

Kernel version reverse-bisect showed that it works with 4.0rc1 and higher. I will do a commit reverse-bisect when I have time.

[Launchpad Janitor (janitor)]

[Expired for linux (Ubuntu) because there has been no activity for 60 days.]

[bademux (bademux)]

I can confirm that brightness controll works on Lubuntu alpha2 - http://cdimage.ubuntu.com/lubuntu/releases/15.10/alpha-2/wily-desktop-amd64.iso

$uname -r
4.1.0.2-generic