boot freeze with kernel 3.13.0-43

Note that ubuntu-bug was run with 3.13.0-40 because I cannot do a normal boot in 3.13.0-43.

I have HD6770 with mesa drivers (r600).

Boot hangs with the Ubuntu logo. Works fine in kernel 3.6.0-40.

If I boot 3.6.0-43 in failsafe X, X starts but I get some dialog boxes with unreadable fonts (or dots, they are so small that it looks just like dots).

Very similar to problem discussed here:
http://askubuntu.com/questions/560350/boot-hangs-after-upgrade-to-kernel-3-13-0-43
where someone reports that it works with fglrx

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: xorg 1:7.7+1ubuntu8
ProcVersionSignature: Ubuntu 3.13.0-40.69-generic 3.13.11.10
Uname: Linux 3.13.0-40-generic x86_64
.tmp.unity.support.test.0:

ApportVersion: 2.14.1-0ubuntu3.6
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: Sun Dec 14 12:53:15 2014
DistUpgraded: Fresh install
DistroCodename: trusty
DistroVariant: ubuntu
ExtraDebuggingInterest: Yes
GpuHangFrequency: Continuously
GpuHangReproducibility: Yes, I can easily reproduce it
GpuHangStarted: Within the last few days
GraphicsCard:
 Advanced Micro Devices, Inc. [AMD/ATI] Juniper XT [Radeon HD 6770] [1002:68ba] (prog-if 00 [VGA controller])
   Subsystem: ASUSTeK Computer Inc. Device [1043:03fe]
InstallationDate: Installed on 2014-03-24 (264 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Alpha amd64 (20140323)
MachineType: To be filled by O.E.M. To be filled by O.E.M.
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.13.0-40-generic root=/dev/mapper/sysvg-lvroot1 ro quiet splash vt.handoff=7
SourcePackage: xorg
Symptom: display
Title: Xorg freeze
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 11/06/2013
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 2103
dmi.board.asset.tag: To be filled by O.E.M.
dmi.board.name: M5A97 R2.0
dmi.board.vendor: ASUSTeK COMPUTER INC.
dmi.board.version: Rev 1.xx
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.:bvr2103:bd11/06/2013:svnTobefilledbyO.E.M.:pnTobefilledbyO.E.M.:pvrTobefilledbyO.E.M.:rvnASUSTeKCOMPUTERINC.:rnM5A97R2.0:rvrRev1.xx: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 1:0.9.11.2+14.04.20140714-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.52-1
version.libgl1-mesa-dri: libgl1-mesa-dri 10.1.3-0ubuntu0.2
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 10.1.3-0ubuntu0.2
version.xserver-xorg-core: xserver-xorg-core 2:1.15.1-0ubuntu2.5
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.8.2-1ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.3.0-1ubuntu3.1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.910-0ubuntu1.3
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.10-1ubuntu2
xserver.bootTime: Sun Dec 14 12:47:56 2014
xserver.configfile: default
xserver.errors:

xserver.logfile: /var/log/Xorg.0.log
xserver.version: 2:1.15.1-0ubuntu2.5
xserver.video_driver: radeon