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    SubjectRe: [PATCH 9/9] x86: Detect whether we should use Xen SWIOTLB.
    > > >>> Is there any way we can abstract this out a bit more instead of crapping
    > > >>> on generic code?
    > > >
    > > > I don't like this change much too, however I think that this is the
    > > > most simple and straightforward.
    > > >
    > > > Basically, Xen's swiotlb works like a new IOMMU implementation so we
    > > > need to initialize it like other IOMMU implementations (call the
    > > > detect and init functions in order).
    > > >
    > >
    > > Even mentioning "xen" in generic code should be considered a bug. I
    > > think we *do* need to driverize the iommu stuff, and yes, Xen's swiotlb
    > > should just be handled like one in the list.

    I think we all don't like the way 'pci_iommu_alloc' does it. But it does
    the job right now pretty well, and the code looks well, ok. Adding in
    the extra '_detect' and '_init' does not detract from it all that much.

    Long term I think the driverization is the way to go, and..

    > > > I really don't think that this makes the code better. I prefer the
    > > > current simple (dumb) code.
    > > >
    > >
    > > The special handling of swiotlb here really looks wrong, but otherwise I
    > > think it's the right idea.
    > >
    > > > Even if SWIOTLB works, we see if hardware IOMMU is available. SWIOTLB
    > > > is a last resort. We prefer hardware IOMMU.
    > >
    > > Any reason to not just handle swiotlb like any of the other iommus, at
    > > the bottom of the list?
    >
    > we need to check if swiotlb usage is forced by the command line since:
    >
    > - we skip hardware IOMMU initialization if so.

    I think the flow a). check if we need SWIOTLB b), check all IOMMUs, c).
    recheck SWIOTLB in case no IOMMUs volunteered MUST be preserved
    irregardless if we driverize the IOMMUs/SWIOTLB or not.

    Perhaps we should get together at one of these Linux conferences and
    think this one through? Beers on me.



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