linux-kernel - Re: [PATCH 2.6.24-rc1] fix sg_phys to use dma_addr

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Date:	Thu, 25 Oct 2007 11:00:24 +0200
From:	Rolf Eike Beer <eike-kernel@...tec.de>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Hugh Dickins <hugh@...itas.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.6.24-rc1] fix sg_phys to use dma_addr_t

Jens Axboe wrote:
> On Thu, Oct 25 2007, Rolf Eike Beer wrote:
> > Am Donnerstag, 25. Oktober 2007 schrieb Arjan van de Ven:
> > > > Signed-off-by: Hugh Dickins <hugh@...itas.com>
> > > > ---
> > > > Whether this is a complete patch, suitable for all architectures,
> > > > I'm not sure: it builds, boots and runs correctly on the x86_32 box
> > > > in question, but you'll be a lot wiser than me about using dma_addr_t
> > > > for everyone.  (Seems a bit of a shame to include <asm/types.h> here,
> > > > when I think all arches already get to include it one way or another,
> > > > typically via asm/scatterlist.h; but I guess it's safest to repeat
> > > > it.)
> > >
> > > there is a problem with this... sg_phys doesn't return an actual *dma*
> > > address.... at least not an address you can give to the device.
> > > Using dma_addr_t is thus a bit misleading.....
> >
> > Ok, then: how do I actually get such an address?
>
> You use the dma mapping api, Documentation/DMA-mapping.txt

Which comes back always to the same point: if I get a buffer from userspace to 
use for DMA: what can I do then? I need to convert a given list of (physical, 
pinned) pages to DMA addresses.

Eike

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