Login screen invisible / UI hanging when both 4K monitors connected via Displayport MST (docking station)

[Nicolas Ramoudt]

I am experiencing serious issues after upgrading to Ubuntu 17.10 (coming from 17.04 with Gnome, kernel 4.13).

I have 2 x 4K (Asus PB279Q) monitors, connected to a Lenovo Ultra Dock (containing 2 x Displayport via MST), where the Lenovo T550 is connected onto it. Both monitors were working perfectly fine at 30Hz simultaneously in an extended desktop, 4K resolution in my old setup with Gnome for over half a year (since kernel 4.10 blink issues on 4K were solved, i used this setup since then).

However after upgrading to 17.10 using the new Gnome interface:
When the laptop is connected to the Lenovo Ultra Dock (to work on both monitors), the system is hanging and becoming unresponsive. The mouse pointer is freezing and the only way is to do a hard-reboot. I have checked the monitor settings, it's displayed at 60Hz when active, and it appears I am never able to use both monitors simultaneously. When I get 1 monitor working (disconnecting the 2nd monitor from the MST port), after rebooting it works fine. I tried to put settings of the 4K manually on 30Hz, reconnecting, but the system hangs again. I have tried several combinations. It results in a blank (purple) screen and hanging mouse (see attachment).

I tried also with the installation-iso to run a fresh 17.10 and tried the same, the symptoms are similar. I suspect that must be an issue with the Displayport MST on dual 4K setups in the new 17.10.

When I connect 1 x 4K monitor to the rear displayport of the Lenovo Ultra Dock (there are 2 for MST on the rear, so I disconnected the other) *and* when I connect the other 4K monitor on the separate displayport of the T550 itself instead, it works 100% fine!

Shortly: based on my knowledge that must definitely be some issue with the MST displayport functionality itself, that is unable to recognize/identify both 4K monitors when connected to the dock's both displayport connections?

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: xorg 1:7.7+19ubuntu3
Uname: Linux 4.13.4-041304-generic x86_64
.tmp.unity_support_test.0:

ApportVersion: 2.20.7-0ubuntu3
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: None
CurrentDesktop: ubuntu:GNOME
Date: Fri Oct 20 21:10:50 2017
DistUpgraded: 2017-10-19 21:54:53,162 DEBUG icon theme changed, re-reading
DistroCodename: artful
DistroVariant: ubuntu
ExtraDebuggingInterest: I just need to know a workaround
GraphicsCard:
 Intel Corporation HD Graphics 5500 [8086:1616] (rev 09) (prog-if 00 [VGA controller])
   Subsystem: Lenovo HD Graphics 5500 [17aa:2225]
   Subsystem: Lenovo GM108M [GeForce 940M] [17aa:2225]
InstallationDate: Installed on 2017-04-16 (186 days ago)
InstallationMedia: Ubuntu 17.04 "Zesty Zapus" - Release amd64 (20170412)
MachineType: LENOVO 20CKCTO1WW
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.13.4-041304-generic root=UUID=9fcc7f4c-35c0-4297-9c98-4dac9acee798 ro quiet splash vt.handoff=7
SourcePackage: xorg
Symptom: display
UpgradeStatus: Upgraded to artful on 2017-10-19 (0 days ago)
dmi.bios.date: 09/13/2017
dmi.bios.vendor: LENOVO
dmi.bios.version: N11ET42W (1.18 )
dmi.board.asset.tag: Not Available
dmi.board.name: 20CKCTO1WW
dmi.board.vendor: LENOVO
dmi.board.version: SDK0E50512 STD
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: None
dmi.modalias: dmi:bvnLENOVO:bvrN11ET42W(1.18):bd09/13/2017:svnLENOVO:pn20CKCTO1WW:pvrThinkPadT550:rvnLENOVO:rn20CKCTO1WW:rvrSDK0E50512STD:cvnLENOVO:ct10:cvrNone:
dmi.product.family: ThinkPad T550
dmi.product.name: 20CKCTO1WW
dmi.product.version: ThinkPad T550
dmi.sys.vendor: LENOVO
version.compiz: compiz 1:0.9.13.1+17.10.20170901-0ubuntu1
version.libdrm2: libdrm2 2.4.83-1
version.libgl1-mesa-dri: libgl1-mesa-dri 17.2.2-0ubuntu1
version.libgl1-mesa-glx: libgl1-mesa-glx 17.2.2-0ubuntu1
version.xserver-xorg-core: xserver-xorg-core 2:1.19.5-0ubuntu2
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.10.0-1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20170309-0ubuntu1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.15-2
xserver.bootTime: Mon Apr 17 17:36:46 2017
xserver.configfile: default
xserver.logfile: /var/log/Xorg.0.log
xserver.version: 2:1.19.3-1ubuntu1
xserver.video_driver: modeset

[Nicolas Ramoudt (smoetje)]

Update:

I did a full 17.10 reinstall as last attempt.
I can confirm the following symptoms:
- When both 4k displays are connected to the docking (displayport MST), UI login screen is already hanging (see earlier screenshot)
- When 1 x 4K display is connected it works. When connecting 2nd display after login (using Wayland), the UI is completely hanging

[Daniel van Vugt (vanvugt)]

Thank you for reporting this bug to Ubuntu.
Ubuntu 17.10 (artful) reached end-of-life on July 19, 2018.

See this document for currently supported Ubuntu releases:
https://wiki.ubuntu.com/Releases

We appreciate that this bug may be old and you might not be interested in discussing it any more. But if you are then please upgrade to the latest Ubuntu version and re-test. If you then find the bug is still present in the newer Ubuntu version, please add a comment here telling us which new version it is in and change the bug status to Confirmed.