I had this issue chew up my saturday, managed to fix it though.
Posting it here hoping that it may be useful:
: nvidia 9600 GT, on an Intel DP43TF, 4GB RAM installed
: x86 FreeBSD 7.1-RELEASE, X.Org 1.5.3, nvidia driver 180.29
: system locks up when starting X.
Specifically, the following message is printed twice during X startup:
NVIDIA: failed to set MTRR 0xc0000000, 0M (write-combining)
Also, startup is excessively slow, with at least a minute pause after monitor EDID is read.
When the screen is finally initialized, (as seen by an X log message about the logo getting loaded),
kernel: NVRM: Xid (0001:00): 6, PE0001
and the system locks up shortly afterwards.
I suspect this is due to address space issues.
It occurs when my (32-bit, non-PAE) system is booted with 4GB of memory installed,
and vanishes when I boot with 2GB of memory.
Interestingly, this issue is NOT fixed if I boot with hw.physmem=2GB,
and 4GB installed in the machine. The issue must probably be
with memory maps the kernel gets from the BIOS, I guess.
This issue is strange and frustrating enough that it could probably be added as "known issue",
or if it is easily reproducable and not too hard to detect in the driver,
a better warning message (or even making it an actual error) may be helpful.
Keep up the good work, folks!