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Date: Mon, 31 Jan 2022 09:52:54 -0500
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH v2 1/4] Add virtio Admin Virtqueue
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To: Cornelia Huck <cohuck@redhat.com>
Cc: Max Gurtovoy <mgurtovoy@nvidia.com>, Halil Pasic <pasic@linux.ibm.com>, Jason Wang <jasowang@redhat.com>, virtio-comment@lists.oasis-open.org, Virtio-Dev <virtio-dev@lists.oasis-open.org>, Parav Pandit <parav@nvidia.com>, Shahaf Shuler <shahafs@nvidia.com>, Oren Duer <oren@nvidia.com>, Stefan Hajnoczi <stefanha@redhat.com>
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On Mon, Jan 31, 2022 at 03:26:36PM +0100, Cornelia Huck wrote:
> On Mon, Jan 31 2022, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Mon, Jan 31, 2022 at 10:16:43AM +0100, Cornelia Huck wrote:
> >> On Sun, Jan 30 2022, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> >> 
> >> > On Sun, Jan 30, 2022 at 05:12:46PM +0200, Max Gurtovoy wrote:
> >> >> #define VIRTIO_PCI_CAP_MISC_CFG 10
> >> >> 
> >> >> and
> >> >> 
> >> >> struct virtio_pci_misc_cfg {
> >> >>     le16 admin_queue_index; /* read-only for driver */
> >> >> };
> >> >> 
> >> >> Is agreed by all for V3 ? instead of the net and blk AQ index definitions.
> >> >
> >> > We need to add it to MMIO and CCW I guess too.
> >> 
> >> That seems ok for pci.
> >> 
> >> For ccw, I'd do something like
> >> 
> >> #define CCW_CMD_READ_MISC_CONF 0x82
> >> 
> >> struct virtio_misc_conf {
> >>        be16 admin_queue_index;
> >> };
> >> 
> >> bound to revision 3, which gets a payload data containing the length of
> >> this structure (for future expansions).
> >> 
> >> Halil, do you think that would work?
> >> 
> >> For mmio, I'd need to think a bit more. Any mmio experts around?
> >
> > Not an expert but I think we can rely on a feature
> > bit to be acked since admin vq is only needed
> > after feature negotiation is complete.
> 
> You mean a register that is valid conditionally? I don't see an easy way
> to add some kind of "misc" interface for mmio, unlike for the other
> transports.
> 
> So something like:
> 
> AdminQueueIndex/0x0c4/R
> If VIRTIO_F_ADMIN_VQ has been negotiated, reading from this register
> returns the queue index of the administration virtqueue.

No, I mean a register that switches 100+ between device specific
and misc space.

-- 
MST