I'm about to test patches. But before, as promised, here are the values
retrieved read and written to the registers. By the way, I have only a single
monitor.
tmp = RREG32(EVERGREEN_CRTC_CONTROL + crtc_offsets[i]); -> 272696081 (0001 0000
0100 0001 0000 0011 0001 0001)
tmp |= EVERGREEN_CRTC_DISP_READ_REQUEST_DISABLE; -> 289473297 (0001 0001 0100
0001 0000 0011 0001 0001)

So, it is set as you explained me earlier. I'll be back soon with some news
from the patches.