Re: [PATCH v2 1/4] Add virtio Admin Virtqueue

[Cornelia Huck <cohuck@redhat.com>]

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.