Lenovo T450s/T550 don't switch external monitor on after resuming in docking station

[Cs-gon]

After updating 14.04 systems to the Wily HWE stack, the notebooks often fail to switch on external monitors when resuming (after a suspend) them inside the docking station.

Here are the steps I did:

- dock the notebook in the docking station, with an external monitor connected (they are then in a side-by-side mode, not clone mode)
- suspend the notebook (in this case I used the menu entry in the top right Unity menu)
- resume the notebook

Expected results:

On resume the external monitor should be switched on and the display configuration I had before suspending should be restored.

Actual result:

On resume the external monitor is not switched on, although the kernel seems to think it is switched on (based on the xrandr output, which I will also attach to this bugreport).

To get the monitor to switch on, I have to first switch it off, and then switch is on again (using xrandr or the system-settings GUI, both work). After doing that (e.g. xrandr --output DP2-2 --off followed by xrandr --output DP2-2 --mode 1920x1200) the displays are now in "clone" mode (I think it isn't really a clone mode, but the displays don't have any offset to each other). The same happens when using the system-settings GUI.

I have reproduced the above steps with drm.debug=0x1e. I hope this helps.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: linux-image-generic-lts-wily 4.2.0.30.24
ProcVersionSignature: Ubuntu 4.2.0-30.36~14.04.1-generic 4.2.8-ckt3
Uname: Linux 4.2.0-30-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.19
Architecture: amd64
Date: Thu Mar 3 17:11:52 2016
InstallationDate: Installed on 2016-03-03 (0 days ago)
InstallationMedia: Ubuntu 14.04.4 LTS "Trusty Tahr" - Release amd64 (20160217.1)
SourcePackage: linux-meta-lts-wily
UpgradeStatus: No upgrade log present (probably fresh install)

[Cs-gon (cs-gon)]

Hmm, seems apport did not attach the logs, so this is the syslog from the system.

The interesting suspend/resume cycle is around Mar 3 17:03:38.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.