When attempting to use Nouveau driver with Xorg on my SunBlade 2500 running the
latested build from Debian-9.0 Sid SPARC64 CPU 0 runs up to 100% and then
eventually the Xorg session shuts down. It appears that it's timing out on a
GPU lock. A bunch of messages appears in the Xorg.0.log indicating fifo:
CACH_ERROR also with in the messages log there are several repeating errors.

log_unaligned: 598 callbacks suppressed
Kernel unaligned access at TPC[105d9fb4] nvkm_instobj_wr32+0x14/0x20 [nouveau]

Eventually the Xorg session gives up and times out.

I'll try and attach some more logs but it appears to have something to do with
the iowrite32_native macro on SPARC V9 systems.