Created attachment 91835 [details] [review]
Disable the DMA ring in R6xx

Hi, I've got an RV620 (HD3450/3470, pci id 1002:95c4). It usually worked with
dpm, but hanged on boot maybe 1/10 times. I've been testing the dpm-reorder
branch (now drm-next-3.14) and I haven't seen it hang since then.

However, with this branch I got the following:
[drm:r600_dma_ring_test] *ERROR* radeon: ring 3 test failed (0xCAFEDEAD)
and acceleration got disabled. This starts happening with "drm/radeon/pm: move
pm handling into the asic specific code".

I think the DMA ring is not used by mesa nor xf86-video-ati so I changed the
kernel to skip initialisation of the DMA ring and keep acceleration and with
that I've had it working every time (can suspend/resume as well).

I can't be sure this is the cause as the hangs are random, but the results seem
promising so far.