linux-kernel - Re: [PATCH] intel-iommu: Obey coherent_dma_mask for alloc

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Message-ID: <1257480548.2837.121.camel@2710p.home>
Date:	Thu, 05 Nov 2009 21:09:08 -0700
From:	Alex Williamson <alex.williamson@...com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	dwmw2@...radead.org, iommu@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] intel-iommu: Obey coherent_dma_mask for alloc_coherent
 on	passthrough

On Fri, 2009-11-06 at 12:34 +0900, FUJITA Tomonori wrote:
> On Thu, 05 Nov 2009 20:19:52 -0700
> Alex Williamson <alex.williamson@...com> wrote:
> > On Fri, 2009-11-06 at 11:41 +0900, FUJITA Tomonori wrote:
> >
> > > This is fine for 2.6.32 but we'll cleanly fix this by using
> > > swiotlb_dma_ops later, right?
> > 
> > I'm open to suggestions.  I don't really understand why we dropped
> > swiotlb for passthrough mode in 2.6.32 to start with.  It seems like we
> > now have a couple corner cases where we have to either hope for the best
> > or effectively ignore the request to use passthrough.  Thanks,
> 
> I think that the cleanest solution is setting up swiotlb_dma_ops for
> passthrough devices (and devices not behind pci, etc). Calgary IOMMU
> does the same for years.

intel-iommu was using swiotlb for the global dma_ops when in passthrough
mode until 19943b0e (2.6.31 and earlier).  I would say the next step
would be to use per device dma_ops so we can point passthrough devices
to swiotlb, as you suggest, but that seems to work against part of what
19943b0e was trying to accomplish.

Alex

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