Comment # 46 on bug 59431 from Vladimir

I found the exact commit that causes this bug

http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-quantal.git;a=commit;h=8f53b5444a25b5be3bfe0164316f9bc7845279c9

drm/radeon: properly handle mc_stop/mc_resume on evergreen+ (v2)

BugLink: http://bugs.launchpad.net/bugs/1091251

commit 62444b7462a2b98bc78d68736c03a7c4e66ba7e2 upstream.

- Stop the displays from accessing the FB
- Block CPU access
- Turn off MC client access

This should fix issues some users have seen, especially
with UEFI, when changing the MC FB location that result
in hangs or display corruption.

v2: fix crtc enabled check noticed by Luca Tettamanti

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
[ herton: adjust context ]
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>

Hope you guys can fix it