[Thinkpad T420s] Brightness dims when unplugging external monitor and cannot be changed afterwards

[Ara Pulido]

Steps to reproduce

1) Plug a T420s to an external monitor using Displayport
2) Both external and internal monitor look right
3) Unplug (via software or hardware) the external monitor

Expected results:
The brightness in the internal monitor stays the same and it can be changed through system keys or system settings

Actual results:
The brightness in the internal monitor dims and it cannot be changed until the system is rebooted

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: linux-image-3.13.0-6-generic 3.13.0-6.23
ProcVersionSignature: Ubuntu 3.13.0-6.23-generic 3.13.0
Uname: Linux 3.13.0-6-generic x86_64
ApportVersion: 2.13.2-0ubuntu2
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: ara 2409 F.... pulseaudio
CurrentDesktop: Unity
Date: Tue Feb 4 09:06:02 2014
HibernationDevice: RESUME=UUID=85ebfa4c-a925-4edf-9764-79ecfaa29ae6
InstallationDate: Installed on 2013-06-17 (231 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
MachineType: LENOVO 4171CTO
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-6-generic root=UUID=35693a74-fe03-4399-920c-24bfaf0a5649 ro quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-3.13.0-6-generic N/A
 linux-backports-modules-3.13.0-6-generic N/A
 linux-firmware 1.123
SourcePackage: linux
UpgradeStatus: Upgraded to trusty on 2014-01-20 (14 days ago)
dmi.bios.date: 07/11/2012
dmi.bios.vendor: LENOVO
dmi.bios.version: 8CET54WW (1.34 )
dmi.board.asset.tag: Not Available
dmi.board.name: 4171CTO
dmi.board.vendor: LENOVO
dmi.board.version: Not Available
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Not Available
dmi.modalias: dmi:bvnLENOVO:bvr8CET54WW(1.34):bd07/11/2012:svnLENOVO:pn4171CTO:pvrThinkPadT420s:rvnLENOVO:rn4171CTO:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable:
dmi.product.name: 4171CTO
dmi.product.version: ThinkPad T420s
dmi.sys.vendor: LENOVO

[Brad Figg (brad-figg)]

This change was made by a bot.

[Joseph Salisbury (jsalisbury)]

Did this issue just start happening after a recent upgrade or update? If so, we can perform a bisect to identify the commit that introduced this bug.

Also, would it be possible for you to test the latest mainline kernel which is 3.14-rc1? It can be downloaded from:
http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.14-rc1-trusty/

[Ara Pulido (ara)]

This is happening since I upgraded from saucy to trusty.

Installing the latest mainline kernel from http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.14-rc1-trusty/ solves the issue.

[Joseph Salisbury (jsalisbury)]

Thanks for testing and the update. That is good news that the bug is fixed in 3.14-rc1. Can you also test the latest 3.13 stable kernel, which is 3.13.1? It can be downloaded from:

http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.13.1-trusty/

That is the kernel currently in -proposed. So if the bug is fixed there, it will land in Trusty shortly. If the bug is not fixed in 3.13.1, we can perform a reverse bisect to identify the fix in 3.14-rc1.

[Ara Pulido (ara)]

Thanks Joseph.

I have bug is still present in the 3.13.1 kernel. Let's go through that bisect.

[Joseph Salisbury (jsalisbury)]

The 3.13.2 kernel was also just recently released. Can you give that one a test, to see if the fix from 3.14-rc1 made it to stable already? If not, we can bisect:

http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.13.2-trusty/

[Joseph Salisbury (jsalisbury)]

Thank you for taking the time to file a bug report on this issue.

However, given the number of bugs that the Kernel Team receives during any development cycle it is impossible for us to review them all. Therefore, we occasionally resort to using automated bots to request further testing. This is such a request.

  With the recent release of this Ubuntu release, would like to confirm if this bug is still present. Please test again with the newer kernel and indicate in the bug if this issue still exists or not.

You can update to the latest development kernel by simply running the following commands in a terminal window:

    sudo apt-get update
    sudo apt-get dist-upgrade

If the bug still exists, change the bug status from Incomplete to Confirmed. If the bug no longer exists, change the bug status from Incomplete to Fix Released.

If you want this bot to quit automatically requesting kernel tests, add a tag named: bot-stop-nagging.

 Thank you for your help, we really do appreciate it.