Public bug reported:

I have a Dell UP2414Q 24" 4K display panel. The only way to achieve 60Hz
refresh on it, is to use DisplayPort 1.2 MST.

Due to MST, this results in two screens with 1920x2160 resolution being
exposed to X. In order to get back to a proper rendering where it looks
like a single display, one must either use Xinerama (with NVidia) or
Xorg 3.18 and the new xrandr with support for configuring monitors in
RandR 1.5 (with Intel). In both of these configurations, if the monitor
itself is powered off, the output modes will disappear from xrandr, and
when the monitor is powered back on, it behaves as though no output is
being sent to it over the DisplayPort connection. When connecting with
ssh to debug, running DISPLAY=:0 xrandr says that the two outputs exist,
but no modes are configured, and indeed it does not list any. If
however, instead of powering the monitor off, it is left on while away,
this does not occur upon return, and the display works normally as when
it was left.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: xorg 1:7.7+13ubuntu3
ProcVersionSignature: Ubuntu 4.4.0-12.28-generic 4.4.4
Uname: Linux 4.4.0-12-generic x86_64
.tmp.unity.support.test.0:
 
ApportVersion: 2.20-0ubuntu3
Architecture: amd64
CompizPlugins: No value set for 
`/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: compiz
CompositorUnredirectDriverBlacklist: '(nouveau|Intel).*Mesa 8.0'
CompositorUnredirectFSW: true
CurrentDesktop: Unity
Date: Sat Mar 12 12:26:16 2016
DistUpgraded: 2016-03-10 16:26:10,719 DEBUG failed to SystemUnLock() (E:Not 
locked)
DistroCodename: xenial
DistroVariant: ubuntu
DkmsStatus:
 virtualbox, 5.0.16, 4.4.0-11-generic, x86_64: installed
 virtualbox, 5.0.16, 4.4.0-11-lowlatency, x86_64: installed
 virtualbox, 5.0.16, 4.4.0-12-generic, x86_64: installed
 virtualbox, 5.0.16, 4.4.0-12-lowlatency, x86_64: installed
GraphicsCard:
 Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics 
Controller [8086:0412] (rev 06) (prog-if 00 [VGA controller])
   Subsystem: Micro-Star International Co., Ltd. [MSI] Xeon E3-1200 v3/4th Gen 
Core Processor Integrated Graphics Controller [1462:7919]
InstallationDate: Installed on 2012-10-21 (1237 days ago)
InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Release amd64 (20121017.5)
MachineType: MSI MS-7919
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.4.0-12-generic 
root=UUID=167bf6e1-727f-4db1-b2f9-c496700b301b ro quiet splash vt.handoff=7
SourcePackage: xorg
UpgradeStatus: Upgraded to xenial on 2016-03-10 (1 days ago)
dmi.bios.date: 04/30/2014
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: V1.0
dmi.board.asset.tag: To be filled by O.E.M.
dmi.board.name: Z97M GAMING (MS-7919)
dmi.board.vendor: MSI
dmi.board.version: 1.0
dmi.chassis.asset.tag: To be filled by O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: MSI
dmi.chassis.version: 1.0
dmi.modalias: 
dmi:bvnAmericanMegatrendsInc.:bvrV1.0:bd04/30/2014:svnMSI:pnMS-7919:pvr1.0:rvnMSI:rnZ97MGAMING(MS-7919):rvr1.0:cvnMSI:ct3:cvr1.0:
dmi.product.name: MS-7919
dmi.product.version: 1.0
dmi.sys.vendor: MSI
version.compiz: compiz 1:0.9.12.2+16.04.20160209-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.67-1
version.libgl1-mesa-dri: libgl1-mesa-dri 11.1.2-1ubuntu1
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 11.1.2-1ubuntu1
version.xserver-xorg-core: xserver-xorg-core 2:1.18.1-1ubuntu4
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.10.1-1ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.6.1-1ubuntu2
version.xserver-xorg-video-intel: xserver-xorg-video-intel 
2:2.99.917+git20160218-1ubuntu3
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.12-1build2
xserver.bootTime: Sat Mar 12 11:07:14 2016
xserver.configfile: default
xserver.devices:
 
xserver.logfile: /var/log/Xorg.0.log
xserver.outputs:
 
xserver.version: 2:1.18.1-1ubuntu4

** Affects: xorg (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug compiz-0.9 ubuntu xenial

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https://bugs.launchpad.net/bugs/1556452

Title:
  4K@60Hz DisplayPort 1.2 loses output modes

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