Comment 0 for bug 1467190

I have a Lenovo ThinkPad E540 with an Intel Haswell (4th Gen) HD graphics controller connected to a OneLink Pro Dock. The Dock uses DisplayPort (DP) 1.2 MST (multi stream transport) to provide both a DP and a DVI port. My monitor is connected to the DP.

When I used kernels <= 3.16 audio worked fine, but the monitor would flicker heavily. So I installed linux-lts-vivid (3.19) which fixed the graphics problem (now I can see various DP? outputs in xrandr as opposed to one before), but there is no DP audio output to chose anymore.

I also tested the latest mainline kernel 4.1-rc8, where this bug still exists. To further investigate I got these version's kernel sources, applied 4 patches by Dave Airlie from the intel-gfx mailing list [1] and tested this build (4.1-rc8+), which fixed the problem! I can play sound over DP, the same way I can over HDMI or DP without MST.

I hope it is possible to backport these changes!

[1] haswell displayport MST audio support
    http://www.spinics.net/lists/intel-gfx/msg68973.html

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: linux-image-3.19.0-22-generic 3.19.0-22.22~14.04.1
ProcVersionSignature: Ubuntu 3.19.0-22.22~14.04.1-generic 3.19.8-ckt1
Uname: Linux 3.19.0-22-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.11
Architecture: amd64
CurrentDesktop: Unity
Date: Sun Jun 21 01:44:30 2015
InstallationDate: Installed on 2014-01-06 (530 days ago)
InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1)
SourcePackage: linux-lts-vivid
UpgradeStatus: Upgraded to trusty on 2014-06-12 (373 days ago)