Date: 5 Jan 2004 22:10:16 +0100
Date: Mon, 5 Jan 2004 22:10:16 +0100
From: Andi Kleen <ak@colin2.muc.de>
To: "David S. Miller" <davem@redhat.com>
Cc: Andi Kleen <ak@muc.de>, gibbs@scsiguy.com, linux-kernel@vger.kernel.org,
       linux-scsi@vger.kernel.org
Subject: Re: [BUG] x86_64 pci_map_sg modifies sg list - fails multiple map/unmaps
Message-ID: <20040105211016.GA52683@colin2.muc.de>
References: <2938942704.1073325455@aslan.btc.adaptec.com> <m3brpi41q0.fsf@averell.firstfloor.org> <20040105123509.4bacf670.davem@redhat.com>
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On Mon, Jan 05, 2004 at 12:35:09PM -0800, David S. Miller wrote:
> On Mon, 05 Jan 2004 20:47:19 +0100
> Andi Kleen <ak@muc.de> wrote:
> 
> > Actually I disabled merging by default in the latest x86-64 code,
> > but it can be still enabled by the user using options (it makes some
> > adapters run several percent faster). I would appreciate if you could
> > fix the problem anyways.
> > 
> > I was actually planning to add a BUG() for this. Should do that.
> > There is already one that triggers often when the problem occurs.
> 
> Andi, you must not modify sg->length in any way shape or form.
> 
> The following is legal:
> 
> 	pci_map_sg(..&sg);
> 	pci_unmap_sg(...&sg);
> 	pci_map_sg(..&sg);

Well, on x86-64 it is not legal.

> If you must modify the length field for DMA, you must have a seperate
> dma_length member of the scatterlist structure on your platform, see what
> sparc64 does here.
> 
> If the documentation states this wrongly, it's a doc bug.

The documentation doesn't allow it so I didn't implement it.

-Andi
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