linux-kernel - Re: [PATCH 9/9] x86: Detect whether we should use Xen SWIOTLB.

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Date:	Tue, 3 Aug 2010 00:43:52 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	hpa@...or.com
Cc:	konrad.wilk@...cle.com, fujita.tomonori@....ntt.co.jp,
	jeremy@...p.org, Ian.Campbell@...rix.com, albert_herranz@...oo.es,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	jbarnes@...tuousgeek.org, iommu@...ts.linux-foundation.org,
	tglx@...utronix.de
Subject: Re: [PATCH 9/9] x86: Detect whether we should use Xen SWIOTLB.

On Mon, 02 Aug 2010 08:30:38 -0700
"H. Peter Anvin" <hpa@...or.com> wrote:

> On 08/02/2010 08:25 AM, Konrad Rzeszutek Wilk wrote:
> > hpa, are your concerns that a) inserting a sub-system call in the
> > generic code is not good. Or b) that we have five IOMMUs (counting SWIOTLB in that
> > category) and that we don't jettison from memory the ones we don't need
> > (that would be the primary goal of driverization of those IOMMUs,
> > right?). Or c) we should remove all sub-system detect calls (Calgary, AMD,
> > Intel, AGP) altogether from pci-dma.c and depend more on
> > x86_init.iommu structure (perhaps expend it?)
> 
> Sorry, had to deal with other stuff.
> 
> Basically, a) and c) are the issues, with a) being the more immediate;
> the amount of code left in memory is relatively small and as such I'm
> not too concerned with that aspect specifically.
> 
> With five IOMMUs we're well past the point where we need to have a clean
> and generic interface instead of having everything be ad hoc and
> interdependent.

That's the difficult part because IOMMUs are not
interdependent. Hardware IOMMUs are related with swiotlb. GART and
AMD-IOMMU are too.

We could invent sorta IOMMU register interface and driver-ize IOMMUs
but they can't be interdependent completely.
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