> bus_dma_segment_t
> bus_dma_map(struct uio *uio, int maxsize, int start, int end, int alignment)

Note that I'm assuming the presence of a handle here.  (I believe the
tag should be part of the handle, but that's not relevant to this
subthread.)

> The mapping function will use this to
> determine which map to resolve physical addresses from in the absence
> of DVMA.

Forget I said that.  Thinko.