[virtio-dev] RE: [PATCH v2 0/2] transport-pci: Introduce legacy registers access using AQ

Parav Pandit
2023-05-23T17:28:37Z

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Tuesday, May 23, 2023 2:39 AM

> but I would like us to better
> document how and when does device switch to and from legacy mode, and for
> the switch to be somehow reusable for solutions that are closer to vdpa.
>
To my knowledge vdpa do not have such switch, nor such switch in the spec, nor in the vdpa or PCI device.

> Does enabling legacy commands cause the switch? Or should we add a
> LEGACY_PCI command to enable/disable? I kind of like the second option ...

Some devices may find it helpful to issue this command on the AQ, to say enable your legacy emulation and allocate needed resources.
I guess before getting distracted on this side topic, lets close on the AQ or two register MMIO approach in other email thread.