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    SubjectRe: [RFC, v0 1/3] vfio/platform: add support for msi
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    Hi Vikas,

    On 11/6/20 3:54 AM, Vikas Gupta wrote:
    > Hi Alex,
    >
    > On Thu, Nov 5, 2020 at 12:38 PM Alex Williamson
    > <alex.williamson@redhat.com> wrote:
    >>
    >> On Thu, 5 Nov 2020 11:32:55 +0530
    >> Vikas Gupta <vikas.gupta@broadcom.com> wrote:
    >>
    >>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
    >>> index 2f313a238a8f..aab051e8338d 100644
    >>> --- a/include/uapi/linux/vfio.h
    >>> +++ b/include/uapi/linux/vfio.h
    >>> @@ -203,6 +203,7 @@ struct vfio_device_info {
    >>> #define VFIO_DEVICE_FLAGS_AP (1 << 5) /* vfio-ap device */
    >>> #define VFIO_DEVICE_FLAGS_FSL_MC (1 << 6) /* vfio-fsl-mc device */
    >>> #define VFIO_DEVICE_FLAGS_CAPS (1 << 7) /* Info supports caps */
    >>> +#define VFIO_DEVICE_FLAGS_MSI (1 << 8) /* Device supports msi */
    >>> __u32 num_regions; /* Max region index + 1 */
    >>> __u32 num_irqs; /* Max IRQ index + 1 */
    >>> __u32 cap_offset; /* Offset within info struct of first cap */
    >>
    >> This doesn't make any sense to me, MSIs are just edge triggered
    >> interrupts to userspace, so why isn't this fully described via
    >> VFIO_DEVICE_GET_IRQ_INFO? If we do need something new to describe it,
    >> this seems incomplete, which indexes are MSI (IRQ_INFO can describe
    >> that)? We also already support MSI with vfio-pci, so a global flag for
    >> the device advertising this still seems wrong. Thanks,
    >>
    >> Alex
    >>
    > Since VFIO platform uses indexes for IRQ numbers so I think MSI(s)
    > cannot be described using indexes.
    > In the patch set there is no difference between MSI and normal
    > interrupt for VFIO_DEVICE_GET_IRQ_INFO.
    in vfio_platform_irq_init() we first iterate on normal interrupts using
    get_irq(). Can't we add an MSI index at the end of this list with
    vdev->irqs[i].count > 1 and set vdev->num_irqs accordingly?

    Thanks

    Eric
    > The patch set adds MSI(s), say as an extension, to the normal
    > interrupts and handled accordingly. Do you see this is a violation? If
    > yes, then we`ll think of other possible ways to support MSI for the
    > platform devices.
    > Macro VFIO_DEVICE_FLAGS_MSI can be changed to any other name if it
    > collides with an already supported vfio-pci or if not necessary, we
    > can remove this flag.
    >
    > Thanks,
    > Vikas
    >

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