Intel graphics and DisplayPort: *ERROR* failed to train DP, aborting

I'm on a Lenovo t450s and Xubuntu 16.04. When I connect a monitor via displayport and enable it e.g. using xrandr, nothing shows on the screen (except "no signal"), and the following message shows up in dmesg:

[drm:intel_dp_start_link_train [i915]] *ERROR* failed to train DP, aborting

I've tried upgrading the linux kernel to 4.6.0, but the problem persists. I can connect an external monitor via the docking station, but using the mini displayport does not work. Not sure if related, but connecting multiple monitors using displayport on the docking station produces the same result, sometimes accompanied by a system freeze.

I saw a few bugreports on similar issues, but they seem either outdated or not directly related.

Any ideas? Thanks in advance!

I had the exact same problem on my Thinkpad T420 with Ubuntu 16.04.2 LTS (fresh install, not upgrade from older Ubuntu). I did 2 things and now the DisplayPort seems to work fine (have not got my hand on a docking station to test that though).

Here are what I did:

1. Install graphics driver from Intel
   Download it from here:
   https://01.org/linuxgraphics/downloads/intel-graphics-update-tool-linux-os-v2.0.2
   Install the .deb file, and run intel-graphics-update-tool afterwards.
   (You might need gdebi to make it run properly. Read the above link for details.)

For me, just updating the new graphics driver did not work.

2. Install new kernels
   You can find kernels compiled for Ubuntu here:
   http://kernel.ubuntu.com/~kernel-ppa/mainline/?C=M;O=D
   I installed v4.10.1 and things seems to work fine. You might also try other versions, particularly the drm-intel-nightly one.
   You need to download 3 files: (<arch> is the architecture of your machine, e.g. amd64)
   • linux-headers-<version>.<date-time>_all.deb
   • linux-headers-<version>-generic_<version>.<date-time>_<arch>.deb
   • linux-image-<version>-generic_<version>.<date-time>_<arch>.deb

And then installing a new kernel, reboot, and it worked for me.
(Please adjust the grub menu if necessary.)