Date: Thu, 20 Feb 2003 08:22:02 -0800 From: "Sam Leffler" <sam@errno.com> To: "Andrew Gallatin" <gallatin@cs.duke.edu> Cc: "Mike Silbersack" <silby@silby.com>, "Scott Long" <scott_long@btc.adaptec.com>, <src-committers@FreeBSD.org>, <cvs-src@FreeBSD.org>, <cvs-all@FreeBSD.org> Subject: Re: cvs commit: src/sys/dev/aac aac.c aac_pci.c Message-ID: <0dcd01c2d8fc$33a49ee0$52557f42@errno.com> References: <200302192158.h1JLwYJn025529@repoman.freebsd.org> <20030219161458.T62705@patrocles.silby.com> <20030219181629.A46948@grasshopper.cs.duke.edu> <20030219182122.N62705@patrocles.silby.com> <3E54219C.9030103@btc.adaptec.com> <20030219212343.O64167@patrocles.silby.com> <0d1a01c2d894$c99c0540$52557f42@errno.com> <20030220093631.A48177@grasshopper.cs.duke.edu>
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> Sam Leffler [sam@errno.com] wrote:
> > > On Wed, 19 Feb 2003, Scott Long wrote:
> > >
> > > > busdma has been around since 3.0. It probably needs a couple of
hours
> > > > of work to lock it down.
> > >
> > > Hm, icky. Is anyone in the know wrt busdma looking into handling
that? I
> > > don't think we can get much done in the network drivers without
touching
> > > busdma functions.
> > >
> >
> > Since most bus_dma functions operate on driver-private data locking
drivers
> > will probably be sufficient to start. The only issue I know of is that
> > bus_dmamem_alloc calls contigmalloc; so there may be an issue there
getting
> > out from under Giant.
> >
>
> I'm not the most familiar person with the busdma interface.. but..
> at least for network drivers, bus_dmamem_alloc() is typically called
> for descriptor lists, etc. Eg, data shared with the nic, and is done
> at attach time, right? Its never called from the transmit or recv
> routines.
Correct, for nic drivers you either pre-allocator or you map data associated
with mbufs (or private store if you do jumbograms and set them up as
externally-managed storage).
In general though, unless you pre-allocate memory you may need to use it at
the point where you setup for dma. The ubsec crypto driver currently uses
it when handling asymmetric crypto ops.
Sam
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