large (over 4KB) softc struct. The descriptor array is accessed by
busmaster dma and must be physically contiguous in memory. malloc() of
a block greater than a page is only virtually contiguous, and not
necessarily physically contigious.
contigmalloc() could do this, but that is a bit on the overkill side.
I'm not sure of the origins of the problem report and diagnosis, I learned
of the problem via mail forwarded from Jim Shankland <jas@flyingfox.com>.
Jim said that Matt Thomas's workaround was to reduce the number of
transmit descriptors from 128 to 32, but I was concerned that it might
cost performance. Anyway, this change is my fault, not Jim's. :-)
Reviewed by: davidg
