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SubjectRe: [RFC PATCH 0/3] allow fallback to swiotlb on hw iommu init failures
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On Fri, 23 Oct 2009 23:57:12 -0700
Chris Wright <chrisw@sous-sol.org> wrote:

> > Note that Calgary comment 'falling back to no_iommu' is misleading. It
> > actually falls back to swiotlb or nommu properly.
> >
> > Calgary doesn't set to dma_ops to calgary_dma_ops so it doesn't need
> > to pick up swiotlb_dma_ops.
>
> It does need swiotlb_dma_ops even when calgary init succeeds for the devices
> that aren't behind Calgary to deal w/ the case of those devices having
> dma mask smaller than physical memory (i.e those that don't get device
> specific dma_ops set to calgary_dma_ops).

I know since I wrote that code.


> > > The calgary shouldn't even need to be manually setting up
> > > nommu_dma_ops.
> >
> > Yeah, but it needs because of how the dma startup code works.
>
> Be much better to have the core handle all of this. Basically register
> ops and then put the top one on the stack to actual use. So the
> fallback would be automatic, just pick the top of the stack and go.
> Were you thinking of something along those lines?

I don't know what 'register ops and then put the top one on the stack'
means but it sounds overdoing.

I think that we can handle this issue more simply. I've just posted
the patchset.


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