Subject: Re: LANCE (Am7990) DMA
To: Matt Thomas <>
From: Perry E. Metzger <>
List: tech-net
Date: 10/06/1998 00:50:59
Is there any way we could make the driver let you do this more
flexibly so we could cover both the ISA LANCE case and other more
interesting cases (like LANCE on PCI or the Vax?)

Matt Thomas writes:
> At 09:14 PM 10/5/98 , Jason Thorpe wrote:
> >On Mon, 05 Oct 1998 21:27:53 -0700 
> > Matt Thomas <> wrote:
> >
> > > Am I reading the lance code correctly in that none
> > > of the le drivers actually do DMA directly to/from 
> > > mbufs  but actually have other buffers they DMA with 
> > > and then copy to/from mbufs from those buffers?
> >
> >That's correct... that's the way the driver is currently structured.
> >
> >Note, that's safest for e.g. ISA-based LANCE boards, as well as any boards
> >where it can only DMA to on-board memory.
> So on the VAX 4000/60 where it has a scatter/gather map which can
> allow it to address all of memory (or on the VS2000 which only
> has 14MB of memory), the current driver forces an extra data copy 
> where none is needed.  That's really painful on VAXes which have
> already very slow memory bandwidth.  Maybe that means I really
> can't the MI le driver.  Ugh.
> -- 
> Matt Thomas               Internet:
> 3am Software Foundry      WWW URL:
> Sunnyvale, CA             Disclaimer: I avow all knowledge of this message