Date: Sat, 15 Oct 2011 21:45:23 -0600 From: Warner Losh <imp@bsdimp.com> To: Adrian Chadd <adrian@FreeBSD.ORG> Cc: freebsd-arch@FreeBSD.ORG Subject: Re: newbus bus access routines and bus_space_barrier() Message-ID: <4EEA1F8B-9854-4C5C-A397-95AD454D3680@bsdimp.com> In-Reply-To: <CAJ-VmonJnHyLQJ-kVtMV=X7mq7=wq2MGn9wUqdbEtZ6qXd52rg@mail.gmail.com>
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Usually they are needed, but we get away without them often because they are needed in a limited set of circumstances and we have memory barriers in our locking primitives. Warner On Oct 15, 2011, at 7:48 PM, Adrian Chadd wrote: > Hi all, > > I'm not clued up on the way of the bus API, so please excuse the > newbie questions. > > Nathan and I found that ath(4) wasn't working for a user because of a > missing bus barrier. Ath trips it up because it does lots of loops of > register reads/writes through the bus stream API rather than the > normal bus API. > It does this because it handles the register value swapping in > hardware rather than in software. > > The correct fix is to teach ath(4) to use bus_space_barrier() calls > when doing stream calls, which I can do, but the newbus documentation > points out that both normal and stream bus access doesn't enforce > ordering, and barrier calls are needed. But I don't see lots of > bus_space_barrier() calls everywhere. Why's that? > > Thanks, > > > Adrian > _______________________________________________ > freebsd-arch@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-arch > To unsubscribe, send any mail to "freebsd-arch-unsubscribe@freebsd.org" > >home | help
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