Created attachment 112799 [details]
dmesg booted with drm.debug

The new MSI Hawaii board, used single or 2-headed.
The crash in 
[    5.654006] kernel BUG at drivers/gpu/drm/radeon/radeon_sa.c:321!
[    5.654008] invalid opcode: 0000 [#1] PREEMPT SMP 

The crash is 100% repeatable. The system will boot OK to X with
radeon.modeset=0.
The kernel has added trace to verify the firmware requested.

Unclear about 64-bit behavior, since I am booting a live USB distro.
Distro based on Debian Jessie, with
X.Org X Server 1.16.2.901 (1.16.3 RC 1)
Release Date: 2014-12-09