linux-kernel - Re: iommu dma mapping alignment requirements

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Message-ID: <476AD84E.4000507@opengridcomputing.com>
Date:	Thu, 20 Dec 2007 15:02:06 -0600
From:	Steve Wise <swise@...ngridcomputing.com>
To:	benh@....ibm.com
CC:	Roland Dreier <rdreier@...co.com>, linux-kernel@...r.kernel.org,
	OpenFabrics General <general@...ts.openfabrics.org>,
	Benjamin Herrenschmidt <bherren@....ibm.com>,
	Wen Xiong <wenxiong@...ibm.com>,
	Olof Johansson <olof@...om.net>,
	Paul Mackerras <pmac@....ibm.com>
Subject: Re: iommu dma mapping alignment requirements

Benjamin Herrenschmidt wrote:
> Adding A few more people to the discussion. You may well be right and we
> would have to provide the same alignment, though that sucks a bit as one
> of the reason we switched to 4K for the IOMMU is that the iommu space
> available on pSeries is very small and we were running out of it with
> 64K pages and lots of networking activity.
> 

But smarter NIC drivers can resolve this too, I think, but perhaps 
carving up full pages of mapped buffers instead of just assuming mapping 
is free...

perhaps...
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