linux-kernel - Re: a question on DMA and remapping

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Message-ID: <20111122230019.3304ecdf@bob.linux.org.uk>
Date:	Tue, 22 Nov 2011 23:00:19 +0000
From:	Alan Cox <alan@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Alessandro Rubini <ru@...dd.com>, fujita.tomonori@....ntt.co.jp,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	giancarlo.asnaghi@...com, maddalena.brattoli@...com
Subject: Re: a question on DMA and remapping

> Generalising the existing code to cover more cases isn't a bad thing
> to do.  Others might be able to use it, and they surely won't be able
> to use any cloned-and-owned swiotlb.c.

If you look on the kernel list there has also been some discussion and
work recently towards removing a lot of the duplication between the
iommu devices.

I think really you need to be an actual iommu instance because in
reality you are. Trying to fudge it any other way breaks the moment
someone tries to do a device to device DMA transfer because your
bus/phys mapping seen from your device and the bus/phys mapping seen
from another device into your device do not match as I understand it.

Alan
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