It turned out the issue with the IOMMU was a BIOS setting -- and a totally
unsuspected one at that!  Of course, the AMD IOMMU device is part of the
AGP-GART, and I had never been able to get DRM/DRI working, either.  The
problem with both was one and the same -- I had Fast-writes (FW) enabled
in the AGP Hypertransport configuration.  Turning it off allowed both the 
hardware IOMMU and DRM to work.  As I had earlier figured out that I
couldn't boot with the hardware IOMMU enabled and had to use the software
one, at least past kernel 2.6.15 as they killed the SCSI bouncebuffers for
.16, I tested first with that.  Once I got it working, I had  a good idea
the DRM/DRI would work as well, and so it did!  No more being stuck with
Mesa software 3D!  Hallelujah and much rejoicing!  I had been fighting
with that on and off for quite awhile (over a year, tho it got much more
urgent when I upgraded from a gig to 8 gig of RAM and needed the IOMMU),
and had almost come to believe that part of my mobo chipset was borken.
Glad it wasn't!  =8^)

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman in
http://www.linuxdevcenter.com/pub/a/linux/2004/12/22/rms_interview.html


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