Brightness system settings do not work on Asus Eee PC X101CH

[Nir Soffer]

The brightness system setting page does not effect the display brigthness and does not dispaly the currnet brightness.

To reproduce:

1. Set brightness to 50 using (as root):
echo 50 > /sys/class/backlight/psb-bl/brightness

2. Open System Settings > Brightness and Lock
The slider display 100% (the last set value) instead of 50%

3. Modify the slider
The screen brightness does not change

Further testing show that the brightness slider read and write /sys/class/backlight/acpi_video0/brightness instead of /sys/class/backlight/psb-bl/brightness.

---
ApportVersion: 2.6.1-0ubuntu10
Architecture: i386
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: nirs 2057 F.... pulseaudio
DistroRelease: Ubuntu 12.10
HibernationDevice: RESUME=UUID=4cebec9a-7504-469c-8677-d25304edfd40
InstallationDate: Installed on 2012-06-08 (267 days ago)
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release i386 (20120423)
MachineType: ASUSTeK COMPUTER INC. X101CH
MarkForUpload: True
Package: linux (not installed)
ProcFB: 0 psbfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.5.0-26-generic root=UUID=8a182610-1789-4b8d-b2e3-18f776104030 ro crashkernel=384M-2G:64M,2G-:128M quiet splash vt.handoff=7
ProcVersionSignature: Ubuntu 3.5.0-26.40-generic 3.5.7.6
RelatedPackageVersions:
 linux-restricted-modules-3.5.0-26-generic N/A
 linux-backports-modules-3.5.0-26-generic N/A
 linux-firmware 1.95
Tags: quantal
Uname: Linux 3.5.0-26-generic i686
UpgradeStatus: Upgraded to quantal on 2013-02-22 (7 days ago)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
dmi.bios.date: 01/06/2012
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: X101CH.0501
dmi.board.asset.tag: To be filled by O.E.M.
dmi.board.name: X101CH
dmi.board.vendor: ASUSTeK COMPUTER INC.
dmi.board.version: x.xx
dmi.chassis.asset.tag: 0x00000000
dmi.chassis.type: 10
dmi.chassis.vendor: ASUSTeK COMPUTER INC.
dmi.chassis.version: x.x
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrX101CH.0501:bd01/06/2012:svnASUSTeKCOMPUTERINC.:pnX101CH:pvrx.x:rvnASUSTeKCOMPUTERINC.:rnX101CH:rvrx.xx:cvnASUSTeKCOMPUTERINC.:ct10:cvrx.x:
dmi.product.name: X101CH
dmi.product.version: x.x
dmi.sys.vendor: ASUSTeK COMPUTER INC.

[Nir Soffer (nirsof)]

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[Nir Soffer (nirsof)]

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[Nir Soffer (nirsof)]

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[Nir Soffer (nirsof)]

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[Nir Soffer (nirsof)]

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[Nir Soffer (nirsof)]

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[Nir Soffer (nirsof)]

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[Nir Soffer (nirsof)]

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[Nir Soffer (nirsof)]

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[Nir Soffer (nirsof)]

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[Nir Soffer (nirsof)]

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[Nir Soffer (nirsof)]

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[Nir Soffer (nirsof)]

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[Nir Soffer (nirsof)]

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[Nir Soffer (nirsof)]

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[Nir Soffer (nirsof)]

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[Brad Figg (brad-figg)]

This change was made by a bot.

[Nir Soffer (nirsof)]

Fixed if adding this to the boot parameters:

acpi_osi=Linux acpi_backlight=vendor

But in this mode the system freeze when you try to change the brightness using the hardware keys (Fn + F5, Fn + F6).

[Nir Soffer (nirsof)]

The problem is cause by gsd-backlight-helper - it query udev for "backlight" devices, and then pick the first device with type "firmware", "platform", or "raw".

When running on this mahcine (Asus X101CH), it find these devices:

1. firmware: /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0
2. platform: /sys/devices/virtual/backlight/psb-bl
3. raw: (null)

Then it uses "/sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0", becuase firmware is prefered. This device does effect the display brightness, unless the system is booted with acpi_osi=Linux acpi_backlight=vendor(see above).

This patch change the prefered device to be "platform", using "/sys/devices/virtual/backlight/psb-bl", which fix the brightness slider in system setting application.

[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 v3.8 kernel[0] (Not a kernel in the daily directory) and install both the linux-image and linux-image-extra .deb packages.

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/v3.9-rc1-raring/

[Nir Soffer (nirsof)]

Tested with http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.9-rc1-raring/

No change in reported behavior.

[Nir Soffer (nirsof)]

Tested with kernel 3.9.0-rc1 (http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.9-rc1-raring/), and boot parameters "acpi_osi=Linux acpi_backlight=vendor".

System settings brightness panel does affect brightness, with too issues:
1. lowest brightness is not very low, looks like 20-30% instead of 0.
2. Modifying the slider freeze the machine randomally, requiring hardware reset.