I tested mesa-git on 3.14-rc4 and the problem was almost the same but i was able to jump to terminal after freeze. I cannot test on 3.14-rc5 because their is a problem with btrfs support on root(Their was a problem in rc4 too but compilation btrfs as module helped, in rc5 is not working).
EDIT:
I booted 3.14-rc5, x still don't start but i can switch to terminal.
dmesg 3.14-rc5 mesa: http://pastebin.com/GuyAFzgT
dmesg 3.14-rc5 mesa-git: http://pastebin.com/TSFaacMP
Should I report a bug that mesa bug tracker?
You definitely have all sorts of errors surrounding the card. I would at least check the mesa bug tracker, as well as the ATI and dri stuff as well. There may be useful information at Phoronix as well, but it may be a pain to sift through all of the noise to find it.
There is one thing though. Did you build the new mesa stack yourself or did you use the [mesa-git] repo? I ask because everything is in that repo including updated drivers.
]]>please boot to console mode and post the log of that boot.
(if you normally boot to a display manager / X , append systemd.unit=multi-user.target to your kernel boot line) .
2014-03-05T19:35:08+0100 piotek-pc kernel: Your BIOS doesn't leave a aperture memory hole
2014-03-05T19:35:08+0100 piotek-pc kernel: Please enable the IOMMU option in the BIOS setup
2014-03-05T19:35:08+0100 piotek-pc kernel: This costs you 64 MB of RAM
There are many amd 64-bit linux systems where IOMMU is needed, have you tried enabling IOMMU ?
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