Kernel backlight driver does not physically change the light level

[Janne Moren]

As the subject says: the backlight level on my Panasonic Let's Note CF-S9 stays at full brightness and does not physically change even though the kernel seems to believe it's changing it.

* The backlight buttons work (I get the light level slider thing).

Looking in /sys/class/backlight/panasonic:

> ls
actual_brightness bl_power brightness max_brightness power subsystem uevent

max_brightness = "21", actual brightness = "21", "brightness = "21"

If I pull down the brightness to half using the brightness controls:

max_brightness = "21", actual brightness = "10", "brightness = "10"

** But the light level doesn't actually change **

Same thing if I change it directly:

> sudo sh -c 'echo "5" >brightness'

max_brightness = "21", actual brightness = "5", "brightness = "5"

** again, no physical change in light level **

This affects the CF-S9 machine, and the CF-N9 (same machine with or without a DVD unit). It may affect the CF-Y9 and CF-R9 as well, though their hardware may be somewhat different (different cpu clock).

The main problem really is that at full brightness it is really bright, almost painful at night. Also, it really kills battery life.

WORKAROUND: gksudo gedit /etc/default/grub

(which calls an editor) to replace in the file /etc/default/grub the line:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

with:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi="

Then execute:
$ sudo update-grub && sudo reboot

ProblemType: Bug
DistroRelease: Ubuntu 10.04
Package: linux-image-2.6.32-22-generic 2.6.32-22.33 [modified: lib/modules/2.6.32-22-generic/kernel/drivers/input/tablet/wacom.ko]
Regression: No
Reproducible: Yes
ProcVersionSignature: Ubuntu 2.6.32-22.33-generic 2.6.32.11+drm33.2
Uname: Linux 2.6.32-22-generic x86_64
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.21.
Architecture: amd64
ArecordDevices:
 **** List of CAPTURE Hardware Devices ****
 card 0: Intel [HDA Intel], device 0: HDA Generic [HDA Generic]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: janne 1412 F.... pulseaudio
CRDA: Error: [Errno 2] Filen eller katalogen finns inte
Card0.Amixer.info:
 Card hw:0 'Intel'/'HDA Intel at 0xf4a20000 irq 22'
   Mixer name : 'Intel G45 DEVIBX'
   Components : 'HDA:14f15068,10f70000,00100302 HDA:80862804,80860101,00100000'
   Controls : 9
   Simple ctrls : 4
Date: Thu Jun 3 09:38:58 2010
HibernationDevice: RESUME=UUID=6fd7f6ad-3b8d-4fc4-a6cd-206104a94db9
InstallationMedia: Ubuntu 10.04 LTS "Lucid Lynx" - Release amd64 (20100429)
MachineType: Panasonic Corporation CF-S9JYEBDR
PccardctlIdent:
 Socket 0:
   no product info available
PccardctlStatus:
 Socket 0:
   no card
ProcCmdLine: BOOT_IMAGE=/boot/vmlinuz-2.6.32-22-generic root=UUID=a1f2d382-4e79-41b4-ab46-29ae811e5102 ro quiet splash
ProcEnviron:
 LANGUAGE=sv:en
 PATH=(custom, user)
 LANG=sv_SE.utf8
 SHELL=/bin/bash
RelatedPackageVersions: linux-firmware 1.34
RfKill:
 0: phy0: Wireless LAN
  Soft blocked: no
  Hard blocked: yes
SourcePackage: linux
dmi.bios.date: 03/11/2010
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: V1.00L19
dmi.board.asset.tag: No Asset Tag
dmi.board.name: CFS9-1
dmi.board.vendor: Panasonic Corporation
dmi.board.version: 1
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: Panasonic Corporation
dmi.chassis.version: 001
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrV1.00L19:bd03/11/2010:svnPanasonicCorporation:pnCF-S9JYEBDR:pvr001:rvnPanasonicCorporation:rnCFS9-1:rvr1:cvnPanasonicCorporation:ct10:cvr001:
dmi.product.name: CF-S9JYEBDR
dmi.product.version: 001
dmi.sys.vendor: Panasonic Corporation

[discord (colin.williams)]

why do you have the architecture marked as amd, when it uses and intel chipset?

[Janne Moren (jan-moren-gmail)]

Because the 64-bit x86 architecture is called amd64, as amd originated those extensions? As opposed to the Itanium architecture from Intel which never took off? All the added information here is collected automagically by the ubuntu-bug application, so if that's the wrong name for it you should probably file a bug on whatever tool collected that particular bit of info.

But rest assured it is indeed an Intel cpu and Intel chipset.

[Jeremy Foshee (jeremyfoshee)]

Hi Janne,

If you could also please test the latest upstream kernel available that would be great. It will allow additional upstream developers to examine the issue. Refer to https://wiki.ubuntu.com/KernelMainlineBuilds . Once you've tested the upstream kernel, please remove the 'needs-upstream-testing' tag. This can be done by clicking on the yellow pencil icon next to the tag located at the bottom of the bug description and deleting the 'needs-upstream-testing' text. Please let us know your results.

Thanks in advance.

    [This is an automated message. Apologies if it has reached you inappropriately; please just reply to this message indicating so.]

[Janne Moren (jan-moren-gmail)]

I tested with mainline kernel 2.6.35-999-generic (linux-image-2.6.35-999-generic_2.6.35-999.201006021335_amd64.deb) of 2010-05-31, the latest available build. No difference at all. Same problem.

[Janne Moren (jan-moren-gmail)]

Anything else I can do to help diagnose this?

[Nil (nicolas-limare)]

I experience the same problems with recent Debian kernels.
Bug reported there too: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=587014

[Jonathan Wiltshire (jwiltshire)]

Bug reporter does not confirm that the issue was fixed.

[LucByhet (lucbyhet)]

Same problem here. I'm running 11.04 i686 on my new CF-S9, everything works except brightness control.

Is there anything i can do to help solve this problem?

[Axel G. Rossberg (axel-rossberg)]

A solution for this problem that works for me (ubuntu 10.10,
2.6.35-24 kernel) is described here
http://ubuntuforums.org/showthread.php?t=1612560

In a nutshell, add the kernel option "acpi_osi=" to grub, by executing

$ gksudo gedit /etc/default/grub

(which calls an editor) to replace in the file /etc/default/grub the line

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

with

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi="

Then execute

$ sudo update-grub

and reboot. Backlight-changing should now work seamlessly.

Axel

[Janne Moren (jan-moren-gmail)]

I can confirm that this seems to work. I get the impression that turning it back to "full" doesn't actually take it all the way to the initial maximum brightness, but it's hard to compare - I may well just imagine it. The values in the "backlight" class under /sys certainly thinks it's set at the maximum allowable value.

[penalvch (penalvch)]

Janne Moren, this bug was reported a while ago and there hasn't been any activity in it recently. We were wondering if this is still an issue? Can you try with the latest development release of Ubuntu? ISO CD images are available from http://cdimage.ubuntu.com/releases/ .

If it remains an issue, could you run the following command in the development release from a Terminal (Applications->Accessories->Terminal). It will automatically gather and attach updated debug information to this report.

apport-collect -p linux <replace-with-bug-number>

Also, if you could test the latest upstream kernel available that would be great. It will allow additional upstream developers to examine the issue. Refer to https://wiki.ubuntu.com/KernelMainlineBuilds . Once you've tested the upstream kernel, please remove the 'needs-upstream-testing' tag. This can be done by clicking on the yellow pencil icon next to the tag located at the bottom of the bug description and deleting the 'needs-upstream-testing' text.

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'.

Please let us know your results. Thanks in advance.

[Janne Moren (jan-moren-gmail)]

Christopher, this bug was fixed for me long ago - not sure exactly when, but at least 11.10 worked perfectly out of the box, as does 12.04. Frankly, I'd forgotten I ever filed this bug and had no thought about revisiting it with new information.

[penalvch (penalvch)]

Janne Moren, this bug report is being closed due to your last comment regarding this being fixed with an update. For future reference you can manage the status of your own bugs by clicking on the current status in the yellow line and then choosing a new status in the revealed drop down box. You can learn more about bug statuses at https://wiki.ubuntu.com/Bugs/Status. Thank you again for taking the time to report this bug and helping to make Ubuntu better. Please submit any future bugs you may find.