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

[Parav Pandit <parav@nvidia.com>]

On 5/10/2023 3:43 AM, Michael S. Tsirkin wrote:
> On Wed, May 10, 2023 at 03:01:25PM +0800, Jason Wang wrote:
> > On Wed, May 10, 2023 at 2:05âPM Michael S. Tsirkin <mst@redhat.com> wrote:
> > > On Mon, May 08, 2023 at 10:23:39AM +0800, Jason Wang wrote:
> > > > > I thought so too originally. Unfortunately I now think that no, legacy is not
> > > > > going to be a byproduct of transport virtqueue for modern -
> > > > > it is different enough that it needs dedicated commands.
> > > >
> > > > If you mean the transport virtqueue, I think some dedicated commands
> > > > for legacy are needed. Then it would be a transport that supports
> > > > transitional devices. It would be much better than having commands for
> > > > a partial transport like this patch did.
> > >
> > > OK I am beginning to get what you are saying.  So your criticism is
> > > this: what if device supports vq transport for modern, and we want to
> > > build a transitional device on top.  how will that look. yes?
> >
> > Yes. I think it needs to be done through the transport virtqueue
> > otherwise the transport is not self-contained.
>
> I mean, any feature can be done over transport vq.
>
> But there is value in adding legacy commands to an otherwise
> modern device without reworking it completely to
> switch to a different transport.
Yes.

> > > A reasonable thing to include at least in the commit log. Parav?
> > >
> > > You are also asking what if the device uses transport vq,
> > > and we want transitional on top of that.
> > > It's a fair question but I don't exactly get why would
> > > this legacy support feature be wanted for the vq transport
> > > and not for other transports.
> >
> > Not sure I get the question, but all the existing transport support
> > legacy, if we want to have another, should the legacy support be a
> > must or not?
>
> This specific proposal is for tunneling legacy over admin vq.
> It can live alongside a normal modern VF, with hypervisor
> combining these to create a transitional device.
True.