Comment 11 for bug 912387

Forwarding this bug from Ubuntu reporter Roland Dreier:
http://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/912387

[Problem]
Currently, the login screen is set to mirrored (at a lower resolution). On login, the system reconfigures the displays to their native resolutions, but the external DP monitor just shows black.

The kernel log shows:
[ 382.963872] [drm:intel_dp_complete_link_train] *ERROR* failed to train DP, aborting

[Original Description]
I have a Lenovo t410s laptop (Arrandale graphics) that I use with a docking station that is connected to an external monitor via displayport. I just updated from Oneiric to the latest Precise daily, and I've seen big regressions using this setup. I went into the display control panel and set my monitors to be non-mirrored and set my DP monitor to its native (2560x1440) resolution.

Now, after a cold reboot, the login screen comes up fine (in its bad fallback resolution -- this I think is a known lightdm issue, where a laptop+external monitor ends up with lightdm using some non-native resolution). But then when I log in, X tries to change the mode of the DP monitor to the correct one, and at that point the monitor just goes black. If I do alt-f1 I can get back to a text console, but alt-f7 just goes back to the black screen.

I am able to open my laptop and bring up the LVDS1 output, but I have not been able to figure out how to light up the DP output.

Oneiric was able to handle this pretty well -- if I booted docked, the external monitor was used at its native resolution, and if I booted undocked the internal LVDS was used at its native resolution. And even suspend/resume and docking/undocking usually worked.

I see messages like:

[ 382.963872] [drm:intel_dp_complete_link_train] *ERROR* failed to train DP, aborting

in the kernel log, which are presumably related to the failure to light up the DP monitor.

DistroRelease: Ubuntu 12.04
Package: xserver-xorg-video-intel 2:2.15.901-1ubuntu4
ProcVersionSignature: Ubuntu 3.2.0-7.13-generic 3.2.0-rc7
Uname: Linux 3.2.0-7-generic x86_64
.tmp.unity.support.test.0:

ApportVersion: 1.90-0ubuntu1
Architecture: amd64
CompizPlugins: [core,bailer,detection,composite,opengl,compiztoolbox,decor,resize,gnomecompat,grid,move,snap,vpswitch,place,regex,session,imgpng,mousepoll,animation,wall,expo,unitymtgrabhandles,fade,workarounds,scale,ezoom,unityshell]
CompositorRunning: compiz
Date: Thu Jan 5 08:55:36 2012
DistUpgraded: Fresh install
DistroCodename: precise
DistroVariant: ubuntu
EcryptfsInUse: Yes
ExtraDebuggingInterest: Yes, whatever it takes to get this fixed in Ubuntu
GraphicsCard:
 Intel Corporation Core Processor Integrated Graphics Controller [8086:0046] (rev 02) (prog-if 00 [VGA controller])
   Subsystem: Lenovo Device [17aa:21c1]
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha amd64 (20120104)
MachineType: LENOVO 2901CTO
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.2.0-7-generic root=UUID=677292b2-a7ba-4d9e-8f1a-662c546b62ce ro intel_iommu=igfx_off quiet splash vt.handoff=7
SourcePackage: xserver-xorg-video-intel
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 10/27/2010
dmi.bios.vendor: LENOVO
dmi.bios.version: 6UET61WW (1.41 )
dmi.board.name: 2901CTO
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:bvr6UET61WW(1.41):bd10/27/2010:svnLENOVO:pn2901CTO:pvrThinkPadT410s:rvnLENOVO:rn2901CTO:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable:
dmi.product.name: 2901CTO
dmi.product.version: ThinkPad T410s
dmi.sys.vendor: LENOVO
version.compiz: compiz 1:0.9.6+bzr20110929-0ubuntu8
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.29-1ubuntu1
version.libgl1-mesa-dri: libgl1-mesa-dri 7.11-0ubuntu4
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 7.11-0ubuntu4
version.xserver-xorg-core: xserver-xorg-core 2:1.10.4-1ubuntu6
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.6.0-1ubuntu13
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:6.14.99~git20110811.g93fc084-0ubuntu1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.15.901-1ubuntu4
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:0.0.16+git20111201+b5534a1-1