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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>,
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Subject: Re: cvs commit: src/sys/dev/aac aac.c aac_pci.c
Date: Thu, 20 Feb 2003 08:22:02 -0800
Organization: Errno Consulting
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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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