I was experimenting with reformatting a disk to 1024-byte sectors again today
and I found that the aic7xxx driver had the same problem with overflow in
the timeout calculation that the ncr53c9x driver did.  I fixed that one,
but looking at the other disk drivers in sys/dev/ic, I see these problems:

same timeout problem as the drivers mentioned above:
	adw
	aha
	aic6360
	bha
	mb89352
	ncr5380sbc
	sunscpal

problem with truncation of small values instead of overflow of large values:
	wdc


also, the dpt driver doesn't use the xfer timeout for interrupt-driven i/o
as far as I can tell.  maybe I missed it.

there are no doubt other drivers with the same problem hidden away, these
are just the ones I found.  I don't have the hardware for most of these,
could someone who can test changes take a look at fixing these problems?

thanks,
-Chuck