Subject: Re: bus_dma
To: None <>
From: David Edelsohn <>
List: tech-kern
Date: 06/11/1998 23:04:01
>>>>> "John S Dyson" writes:

John> I believe that there is no reason to cooperate (in that way, I
John> might be disagreeing with Justin.)  So, for once, I agree
John> with you.  Wouldn't it be nice if FreeBSD could just move
John> forward and not tangle with these things anymore? :-).

	You previously have clarified that FreeBSD only is planning to
support a handful of architectures.  Justin's proposed changes may be an
appropriate optimization for those systems.  I am somewhat concerned from
the discussions if the new interface truly is generalizable beyond SCSI

	If this "improvement" works on all of the systems which you plan
to target -- great.  I hope that if you find it does limit the devices or
systems that you can support, that you consider reverting to the NetBSD
interface, which has been shown not to have such limitations, instead of
trying to add more changes to fix the problem.

	So far the bus_dma changes have been justified based on
theoretical arguments and examples using a subset of devices which conform
to a limited interface that matches the design assumptions.  NetBSD does
not want to limit its support to the ones that FreeBSD chooses which is
neither unreasonable nor arrogant.

	I think that FreeBSD is unnecessarily limiting the systems it can
support.  FreeBSD always has focussed on a limited number of platforms and
this is another decision along that line.  If one restricts the domain,
one often can find improvements.  But that is a lot different than saying
that one implementation is better or more efficient.

David Edelsohn                                      T.J. Watson Research Center                                  P.O. Box 218
+1 914 945 4364 (TL 862)                            Yorktown Heights, NY 10598