Re: port-amd64/42980: satalink DMA fails under amd64

[Julian Bourne <julian.bourne%gmail.com@localhost>]

That patch leaves us back where we started:

satalink0:0: unable to create xfer table DMA map for drive 0, error=22
wd0(satalink0:0:0): using PIO mode 4
satalink0:1: unable to create xfer table DMA map for drive 0, error=22
wd1(satalink0:1:0): using PIO mode 4

along with the subsequent performance issues.

Note also, I had the same behaviour with the regular amd64 (non xen);
so it may be that this boundary versus size check is made other places
as well.

I will verify a few things to make sure that I'm not giving you all
the wrong picture here - but I think its more general than just the
xen code.