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    SubjectRe: Programming PASID in IMS entries
    On Wed, Jul 07, 2021 at 10:50:52AM +0200, Thomas Gleixner wrote:
    > Megha,
    >
    > On Wed, Jul 07 2021 at 09:49, Megha Dey wrote:
    > > Per your suggestions during the last meeting, we wanted to confirm the
    > > sequence to program the PASID into the IMS entries:
    > >
    > > 1. Add a PASID member to struct msi_desc (Add as part of a union. Other
    > > source-id's such as Jason's vm-id can be added to it)
    >
    > Yes. Though we also discussed storing the default PASID in struct device
    > to begin with which is then copied to the msi_desc entries during
    > allocation.

    This seems like a pretty good idea, though it requires that the
    device's IRQ code cast the struct device to some driver specific
    subtype, like mdev in this case.

    > > 2. Create an API which device drivers can call, to program the PASID
    > > (PASID provided by the driver) on a per-irq basis. This API is to be
    > > called after msi_domain_alloc_irqs and will write to the corresponding
    > > msi_desc->pasid entry. (Assumption: For now, all devices will have the
    > > same IMS format). for e.g:
    > >
    > > msi_desc_set_pasid (irq, pasid) {
    > >
    > > struct msi_desc *desc = irq_get_msi_desc(irq);
    > >
    > > desc->pasid = pasid;
    > >
    > > }
    >
    > That interface should be opaque probably with an u64 argument so it can
    > be reused for Jason's VM-id. Jason?

    Well, I certainly wouldn't put any IDXD specific words like PASID in
    the general API. The comingling of PASID with the rest of the IRQ
    registers is entirely a device specific choice.

    Most likely something like mlx5 is going to want to associate a
    pointer with the irq, and I believe it could use a struct device just
    fine.

    Jason

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