Main monitor doesn't wake up after system suspend

[Diabolo]

If I lock my Unity session (Super+L) and power down my two monitors using external power switch, when after a few minutes I restore the power to monitors and wake up Ubuntu only my VGA connected LG display wakes up. My main monitor - a DisplayPort connected Dell U2410 wakes up only for a brief moment (it's power led goes blue from yellow) but before any picture would be displayed it goes back to sleep mode (led goes yellow again).

All of this is true only for X session. If I switch to tty1 (Ctrl+Alt+F1) the Dell wakes up correctly and shows tty1. Going back to X (Ctrl+Alt+F7) causes this monitor to go to power save mode again.

The only means for me to get my main display back in X is to restart the computer, as logging in and out of X doesn't help. I have also tried running Displays configuration tool while in X, but what it only does is that once I click "Detect Displays" button Dell's power led goes blue for a brief moment and then immediately back to yellow (power save mode).

I haven't encountered such behavior with Ubuntu 14.04, nor have I experienced right after migrating to 16.04. I believe this regression showed up with some update within the last two weeks.

Both monitors are hooked up to AMD Radeon 5850 graphics card.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: xorg 1:7.7+13ubuntu3
ProcVersionSignature: Ubuntu 4.4.0-22.40-generic 4.4.8
Uname: Linux 4.4.0-22-generic x86_64
.tmp.unity_support_test.0:

ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
BootLog:
 Scanning for Btrfs filesystems
 Ubuntu_Root: clean, 690241/3670016 files, 6292028/14652416 blocks
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 May 21 21:22:43 2016
DistUpgraded: 2016-04-23 22:19:53,020 ERROR got error from PostInstallScript ./xorg_fix_proprietary.py (Failed to execute child process "./xorg_fix_proprietary.py" (No such file or directory))
DistroCodename: xenial
DistroVariant: ubuntu
DkmsStatus:
 virtualbox, 5.0.18, 4.4.0-21-generic, x86_64: installed
 virtualbox, 5.0.18, 4.4.0-22-generic, x86_64: installed
ExtraDebuggingInterest: Yes
GraphicsCard:
 Advanced Micro Devices, Inc. [AMD/ATI] Cypress PRO [Radeon HD 5850] [1002:6899] (prog-if 00 [VGA controller])
   Subsystem: Advanced Micro Devices, Inc. [AMD/ATI] Cypress PRO [Radeon HD 5850] [1002:0b00]
InstallationDate: Installed on 2015-08-22 (272 days ago)
InstallationMedia: Ubuntu 14.04.3 LTS "Trusty Tahr" - Beta amd64 (20150805)
MachineType: MICRO-STAR INTERNATIONAL CO.,LTD MS-7583
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-22-generic root=UUID=a709e3c2-0c9b-4102-8135-3a38cc17bd0b ro quiet splash vt.handoff=7
SourcePackage: xorg
Symptom: display
UpgradeStatus: Upgraded to xenial on 2016-04-23 (27 days ago)
dmi.bios.date: 08/18/2011
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: V1.11
dmi.board.asset.tag: To Be Filled By O.E.M.
dmi.board.name: P55-GD65 (MS-7583)
dmi.board.vendor: MICRO-STAR INTERNATIONAL CO.,LTD
dmi.board.version: 1.0
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: MICRO-STAR INTERNATIONAL CO.,LTD
dmi.chassis.version: 1.0
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrV1.11:bd08/18/2011:svnMICRO-STARINTERNATIONALCO.,LTD:pnMS-7583:pvr1.0:rvnMICRO-STARINTERNATIONALCO.,LTD:rnP55-GD65(MS-7583):rvr1.0:cvnMICRO-STARINTERNATIONALCO.,LTD:ct3:cvr1.0:
dmi.product.name: MS-7583
dmi.product.version: 1.0
dmi.sys.vendor: MICRO-STAR INTERNATIONAL CO.,LTD
version.compiz: compiz 1:0.9.12.2+16.04.20160415-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.67-1
version.libgl1-mesa-dri: libgl1-mesa-dri 11.2.0-1ubuntu2
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 11.2.0-1ubuntu2
version.xserver-xorg-core: xserver-xorg-core 2:1.18.3-1ubuntu2
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.10.1-1ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.7.0-1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20160325-1ubuntu1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.12-1build2
xserver.bootTime: Sat May 21 20:49:42 2016
xserver.configfile: default
xserver.errors:

xserver.logfile: /var/log/Xorg.0.log
xserver.version: 2:1.18.3-1ubuntu2
xserver.video_driver: radeon

[Launchpad Janitor (janitor)]

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

[Paul White (paulw2u)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. We are sorry that we do not always have the capacity to review all reported bugs in a timely manner.

Ubuntu 16.04 (xenial) reached end-of-standard-support on April 29, 2021.

I'm setting the status of this bug to 'Incomplete' as it's not seen any activity for some time. If this bug report has any relevance when using a currently maintained release of Ubuntu then please let us know which one(s) otherwise this bug report can be left to expire in approximately 60 days time.

[Launchpad Janitor (janitor)]

[Expired for xorg (Ubuntu) because there has been no activity for 60 days.]