"acpi_backlight=vendor" needs to be present in kernel cmdline to have backlight working

[Marcin Juszkiewicz]

On my laptop I had to add "acpi_backlight=vendor" into kernel cmdline to get working backlight. This state is since beginning (10.04 + maverick kernels during uds-m).

If I remove that argument then /sys/class/backlight/acpi_video0/ is created instead of 'asus_laptop' one and changing backlight by hardware keys works randomly - pressing BacklightUp does nothing or decrease or increase level (same with BacklightDown key).

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: linux-image-2.6.39-1-generic 2.6.39-1.6
ProcVersionSignature: Ubuntu 2.6.39-1.6-generic 2.6.39-rc6
Uname: Linux 2.6.39-1-generic x86_64
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.24.
Architecture: amd64
ArecordDevices:
 **** List of CAPTURE Hardware Devices ****
 card 0: Intel [HDA Intel], device 0: ALC269 Analog [ALC269 Analog]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: hrw 2993 F.... xfce4-volumed
                      hrw 3012 F.... pulseaudio
Card0.Amixer.info:
 Card hw:0 'Intel'/'HDA Intel at 0xfe9f4000 irq 46'
   Mixer name : 'Intel Cantiga HDMI'
   Components : 'HDA:10ec0269,10431443,00100004 HDA:80862802,80860101,00100000'
   Controls : 15
   Simple ctrls : 8
Date: Tue May 10 18:26:48 2011
HibernationDevice: RESUME=UUID=042b5e75-5bf6-43a9-b93d-957be35f77ec
MachineType: ASUSTeK Computer Inc. UL30A
ProcEnviron:
 SHELL=/bin/bash
 LANG=pl_PL.UTF-8
 LANGUAGE=pl_PL:en
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-2.6.39-1-generic root=/dev/mapper/hostname-rootfs ro loop.max_loop=256 acpi_backlight=vendor loglevel=0 crashkernel=384M-2G:64M,2G-:128M quiet
RelatedPackageVersions:
 linux-restricted-modules-2.6.39-1-generic N/A
 linux-backports-modules-2.6.39-1-generic N/A
 linux-firmware 1.52
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 12/28/2009
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 212
dmi.board.asset.tag: ATN12345678901234567
dmi.board.name: UL30A
dmi.board.vendor: ASUSTeK Computer Inc.
dmi.board.version: 1.0
dmi.chassis.asset.tag: ATN12345678901234567
dmi.chassis.type: 10
dmi.chassis.vendor: ASUSTeK Computer Inc.
dmi.chassis.version: 1.0
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr212:bd12/28/2009:svnASUSTeKComputerInc.:pnUL30A:pvr1.0:rvnASUSTeKComputerInc.:rnUL30A:rvr1.0:cvnASUSTeKComputerInc.:ct10:cvr1.0:
dmi.product.name: UL30A
dmi.product.version: 1.0
dmi.sys.vendor: ASUSTeK Computer Inc.

[Kamal Mostafa (kamalmostafa)]

@Marcin-

You may wish to try my 'linux-kamal-mjgbacklight' PPA:
  https://launchpad.net/~kamalmostafa/+archive/linux-kamal-mjgbacklight
It provides:
1. A patched kernel which supplies a new /sys/class/backlight/intel_backlight (backported bits from 2.6.39 plus an additional yet-to-land-upstream patch). The patched kernel forces "acpi_backlight=vendor" internally (i.e. it disables acpi_video0). I'm hoping that these patches will all land in Oneiric.
2. A patched gnome-power-manager which connects the brightness keys to the new intel_backlight interface.

See also bug LP: #568611, where other users of this PPA have logged their findings.

[Anton Keks (anton-azib)]

On my Toshiba Satellite R830, I can't change brightness after returning from sleep with Fn-keys, but echoing numbers to /sys/class/backlight/intel_backlight/brightness does change the brightness properly.
It seems that Fn keys write to /sys/class/backlight/acpi_video0/brightness, which doesn't do anything.
Perhaps a fix could be made in Unity (or gnome power manager) to prefer intel_brightness if it's available?

[Marco Lackovic (marco-lackovic)]

I had this problem on my HP Folio 13 both on the old Ubuntu 12.10 and the new Ubuntu 13.04.

I have fixed it by editing /etc/default/grub and changing:

GRUB_CMDLINE_LINUX=""

into:

GRUB_CMDLINE_LINUX="acpi_backlight=vendor"

And eventually by running:

sudo update-grub
sudo reboot

During this entire operation the screen was completely dark. In order to see anything I had to put a very bright lamp against the screen.

I don't see how this bug should be a duplicate of bug #568611. This bug is about the screen back-light not working. Bug #568611 is about the screen controls for increasing and reducing brightness not working.

[madbiologist (me-again)]

The original reporter's issue should be solved upstream in the 3.10-rc3 kernel. It contains the following patch:

author Bastian Triller 2013-05-19 11:52:33 (GMT)
committer Rafael J. Wysocki 2013-05-22 23:41:45 (GMT)
commit c8f6d8351ba8c89d5cd4c562552ec7ec29274e31 (patch)
tree 6bfe155bb1f67c0c798428c93520eca8973738cf
parent ec4602a9588a196fa1a9af46bfdd37cbf5792db4 (diff)

ACPI / video: Add "Asus UL30A" to ACPI video detect blacklist

Like on UL30VT, the ACPI video driver can't control backlight correctly on Asus UL30A. Vendor driver (asus-laptop) can work. This patch is to add "Asus UL30A" to ACPI video detect blacklist in order to use asus-laptop for video control on the "Asus UL30A" rather than ACPI video driver.

Signed-off-by: Bastian Triller
Cc: All stable
Signed-off-by: Rafael J. Wysocki

[madbiologist (me-again)]

The abovementioned patch is now also available in the upstream 3.9.5 kernel as commit 4c52865e365e443d2e3ffafb8b41a206d7848e8f

[Julian Wiedmann (jwiedmann)]

Marcin Juszkiewicz,

the commit mentioned in comment #5 has now landed in -updates for precise/quantal/raring. Could you please update your kernel to the latest available version and confirm that this bug is fixed? Thanks.

[Launchpad Janitor (janitor)]

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