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    SubjectRe: [PATCH v6 01/11] iommu: Add dma ownership management interfaces
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    On 2022-02-24 05:29, Lu Baolu wrote:
    > On 2/24/22 1:16 PM, Lu Baolu wrote:
    >> Hi Robin and Jason,
    >>
    >> On 2/24/22 2:02 AM, Jason Gunthorpe wrote:
    >>> On Wed, Feb 23, 2022 at 06:00:06PM +0000, Robin Murphy wrote:
    >>>
    >>>> ...and equivalently just set owner_cnt directly to 0 here. I don't
    >>>> see a
    >>>> realistic use-case for any driver to claim the same group more than
    >>>> once,
    >>>> and allowing it in the API just feels like opening up various potential
    >>>> corners for things to get out of sync.
    >>> I am Ok if we toss it out to get this merged, as there is no in-kernel
    >>> user right now.
    >>
    >> So we don't need the owner pointer in the API anymore, right?
    >
    > Oh, NO.
    >
    > The owner token represents that the group has been claimed for user
    > space access. And the default domain auto-attach policy will be changed
    > accordingly.
    >
    > So we still need this. Sorry for the noise.

    Exactly. In fact we could almost go the other way, and rename owner_cnt
    to dma_api_users and make it mutually exclusive with owner being set,
    but that's really just cosmetic. It's understandable enough as-is that
    owner_cnt > 0 with owner == NULL represents implicit DMA API ownership.

    Cheers,
    Robin.

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