Black screen on startup after HWE stack update on Ubuntu 14.04 LTS [Radeon R7 graphics]

[Matthew Gummess]

After updating the HWE stack on Ubuntu 14.04 LTS, my computer now regularly boots to a black screen upon startup. I briefly see the purple screen (but no plymouth), and then nothing. You can hear the ubuntu drum roll, though, and I can reboot using the alt+Sysrq+B option.

Adding the nomodeset parameter in GRUB offers a solution of sorts, but the computer boots with Gallium 0.4 on llvmpipe graphics, which makes gaming basically impossible. I can still boot regularly using the 3.16.0-77-generic kernel saved in GRUB.

Other info:

1) I tried an Ubuntu live USB stick with both 14.04.5 on it and then 16.04 and got the same problem.
2) My UEFI firmware is up-to-date as of 1 or 2 days ago.
3) The kernel in question is 4.4.0-36-generic.
4) Ubuntu release: 14.04.5 LTS
5) I have never installed the fglrx driver—I have always used the open-source driver.
6) My exact GPU: AMD A10-7700K Radeon R7 (Kaveri).
7) I'm not sure that the dmesg log automatically attached by apport will be helpful because of the "nomodeset" parameter, so I have attached a dmesg log grabbed from a failed boot. With guidance, I can do the same for other relevant logs.

Hope that's helpful!

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: xorg 1:7.7+1ubuntu8.1
ProcVersionSignature: Ubuntu 4.4.0-36.55~14.04.1-generic 4.4.16
Uname: Linux 4.4.0-36-generic x86_64
.tmp.unity.support.test.1:

ApportVersion: 2.14.1-0ubuntu3.21
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: Tue Sep 13 21:46:45 2016
DistUpgraded: 2016-08-26 20:07:12,800 DEBUG enabling apt cron job
DistroCodename: trusty
DistroVariant: ubuntu
ExtraDebuggingInterest: Yes, if not too technical
GraphicsCard:
 Advanced Micro Devices, Inc. [AMD/ATI] Kaveri [Radeon R7 Graphics] [1002:1313] (prog-if 00 [VGA controller])
   Subsystem: ASRock Incorporation Device [1849:1313]
InstallationDate: Installed on 2015-06-24 (447 days ago)
InstallationMedia: Ubuntu 14.04.2 LTS "Trusty Tahr" - Release amd64 (20150218.1)
MachineType: To Be Filled By O.E.M. To Be Filled By O.E.M.
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-36-generic root=UUID=228ea1db-87eb-476d-b97f-5a4a28c618f4 ro nomodeset quiet splash vt.handoff=7
Renderer: Software
SourcePackage: xorg
UpgradeStatus: Upgraded to trusty on 2016-08-27 (18 days ago)
dmi.bios.date: 03/15/2016
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: P2.30
dmi.board.name: FM2A78M-HD+ R2.0
dmi.board.vendor: ASRock
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: To Be Filled By O.E.M.
dmi.chassis.version: To Be Filled By O.E.M.
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrP2.30:bd03/15/2016:svnToBeFilledByO.E.M.:pnToBeFilledByO.E.M.:pvrToBeFilledByO.E.M.:rvnASRock:rnFM2A78M-HD+R2.0:rvr:cvnToBeFilledByO.E.M.:ct3:cvrToBeFilledByO.E.M.:
dmi.product.name: To Be Filled By O.E.M.
dmi.product.version: To Be Filled By O.E.M.
dmi.sys.vendor: To Be Filled By O.E.M.
version.compiz: compiz 1:0.9.11.3+14.04.20160425-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.67-1ubuntu0.14.04.1
version.libgl1-mesa-dri: libgl1-mesa-dri N/A
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx N/A
version.xserver-xorg-core: xserver-xorg-core N/A
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
version.xserver-xorg-video-ati: xserver-xorg-video-ati N/A
version.xserver-xorg-video-intel: xserver-xorg-video-intel N/A
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau N/A
xserver.bootTime: Tue Sep 13 21:07:07 2016
xserver.configfile: default
xserver.errors:
 open /dev/dri/card0: No such file or directory
 open /dev/dri/card0: No such file or directory
 Screen 0 deleted because of no matching config section.
 Screen 0 deleted because of no matching config section.
 AIGLX: reverting to software rendering
xserver.logfile: /var/log/Xorg.0.log
xserver.outputs:

xserver.version: 2:1.18.3-1ubuntu2.2~trusty3

[Matthew Gummess (mgummess)]

Accidentally submitted this bug twice . . . Not sure how to delete the duplicate.

[Hans Joachim Desserud (hjd)]

>Accidentally submitted this bug twice . . . Not sure how to delete the duplicate.

Look for "Mark as duplicate" towards the top on the right side. I've marked this issue as a duplicate of the other.

[Matthew Gummess (mgummess)]

Thanks Hans!