[virtio-dev] Re: [virtio-comment] RE: [PATCH v2 1/2] transport-pci: Introduce legacy registers access commands

Michael S. Tsirkin
2023-05-19T06:06:54Z

On Thu, May 18, 2023 at 03:42:19PM -0400, Michael S. Tsirkin wrote:
> > > Does this sound like a reasonable
> > > compromize to you?
> >
> > Splitting proposed one command to two commands,
> > 1. one for accessing legacy common config
> > 2. second for accessing legacy device specific config
> >
> > seems fine to me as below.
> >
> > So we will have total 5 commands (instead of 3).
> >
> > 1. legacy common config read
> > 2. legacy common config write
> >
> > 3. legacy device config read
> > 4. legacy device config write
> > 5. query device notification area
> >
> > #1 and #3 same cmd signature but different opcode.
> > #2 and #4 same cmd signature but different opcode.
> >
>
> Sounds reasonable. Jason?
>
> notification thing needs more thought I feel though.
> It feels weirdly bolted on, but I can't put my finger
> on what's wrong exactly yet. Will think it over.

So with a fresh mind, at least three things:

1. given driver attaches to the PF, it should be possible to forward
notifications there, as opposed to individual VFs. NumVFs is 16 bit so
it will fit in a 32 bit write together with VQ index.

2. It should be possible to send notifications through an admin command too,
otherwise admin commands are an incomplete set of functionality.

3. I feel using a capability to describe legacy notification
area would be better just because we already have a
structure for this. make it an express capability if you like.

--
MST