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    SubjectRe: [PATCH v4 0/6] virtio core DMA API conversion
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    On Tue, 2015-11-10 at 11:27 +0100, Joerg Roedel wrote:
    >
    > You have the same problem when real PCIe devices appear that speak
    > virtio. I think the only real (still not very nice) solution is to add a
    > quirk to powerpc platform code that sets noop dma-ops for the existing
    > virtio vendor/device-ids and add a DT property to opt-out of that quirk.
    >
    > New vendor/device-ids (as for real devices) would just not be covered by
    > the quirk and existing emulated devices continue to work.

    Why woud real devices use new vendor/device IDs ? Also there are other
    cases such as using virtio between 2 partitions, which we could do
    under PowerVM ... that would require proper iommu usage with existing
    IDs.

    > The absence of the property just means that the quirk is in place and
    > the system assumes no translation for virtio devices.

    The only way that works forward for me (and possibly sparc & others,
    what about ARM ?) is if we *change* something in virtio qemu at the
    same time as we add some kind of property. For example the ProgIf field
    or revision ID field.

    That way I can key on that change.

    It's still tricky because I would have to somewhat tell my various firmwares
    (SLOF, OpenBIOS, OPAL, ...) so they can create the appropriate property, it's
    still hacky, but it would be workable.

    Ben.



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