AMD SUMO vs Xorg 7.7

[Alexander Konotop]

Hello! It looks like I've found a radeon driver bug.

Distro:
Debian Sid(Unstable).

Hardware:
* SUMO (integrated in AMD A4 APU)
* CAICOS (external)

Problem:
All webkit browsers freeze in few moments after startup while loading/opening or closing tabs.
It happens only whith an integrated card (SUMO).
Either propagating --disable-gpu to a browser or running on CAICOS using DRI_PRIME=1 eliminates
freezing.
Also running sauerbraten on SUMO causes freezing in few seconds after game starts, in menu.
Switching to a terminal and back (ctrl+alt+f1 and then ctrl+alt+f7) unfreezes the game for few
seconds and then it freezes again.
No problems for sauerbraten with DRI_PRIME=1 on CAICOS.

Here's a forum topic which I started before I determined that the browsers problem is caused by
videocard:
https://forum.siduction.org/index.php?topic=6469
But there's not much useful debug info actually.