From owner-freebsd-current  Wed Oct  9 14:10:54 2002
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Date: Thu, 10 Oct 2002 07:20:51 +1000 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: Nate Lawson <nate@root.org>
Cc: Andrew Gallatin <gallatin@cs.duke.edu>, <current@FreeBSD.ORG>
Subject: Re: alpha tinderbox failure
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On Wed, 9 Oct 2002, Nate Lawson wrote:

> On Wed, 9 Oct 2002, Andrew Gallatin wrote:
> > ...
> > Clashing with int nsegments:
> >
> > Sparc64 has the same problem.  ia64 gets around it by just making
> > BUS_SPACE_UNRESTRICTED an int:
> >
> > #define BUS_SPACE_UNRESTRICTED (~0)
> >
> > I'd like to do the same for alpha.   I think this is valid, as
> > BUS_SPACE_UNRESTRICTED seems to be used exlusively as an argument
> > to bus_dma_tag_create(... nsegments = BUS_SPACE_UNRESTRICTED...)
>
> Yes, I looked into this before and agree this is a valid approach.  It's
> likely the number of segments never exceeds 32, let alone 2^31.

However, it is likely that the number of segments exeeds ~0 (which is
-1 on normal 2's complement machines).

bus_dma_tag_create() has a bogus interface.  It takes an "int nsegments"
arg but corrupts it immediately to a "u_int nsegments" struct member.

BUS_SPACE_UNRESTRICTED seems to be used as a generic (null) limit in
at least the isp driver.  It is not clear that ~0 has the correct
overflow and sign extension behaviour for this.

~0UL works better as a generic limit.  It even points to the bogus interface.

Bruce


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