RE: [virtio-comment] RE: [PATCH v6 4/4] transport-pci: Introduce group legacy group member config region access

[Parav Pandit <parav@nvidia.com>]

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Wednesday, June 21, 2023 4:31 PM
> To: Parav Pandit <parav@nvidia.com>
> Cc: virtio-comment@lists.oasis-open.org; cohuck@redhat.com;
> david.edmondson@oracle.com; virtio-dev@lists.oasis-open.org;
> sburla@marvell.com; jasowang@redhat.com; Yishai Hadas
> <yishaih@nvidia.com>; Maor Gottlieb <maorg@nvidia.com>; Shahaf Shuler
> <shahafs@nvidia.com>
> Subject: Re: [virtio-comment] RE: [PATCH v6 4/4] transport-pci: Introduce group
> legacy group member config region access
> 
> On Wed, Jun 21, 2023 at 08:22:58PM +0000, Parav Pandit wrote:
> >
> >
> > > From: Michael S. Tsirkin <mst@redhat.com>
> > > Sent: Wednesday, June 21, 2023 4:06 PM
> >
> > [..]
> > > > > To put it in our terms, something like this:
> > > > > 	when a legacy driver accesses a member device of
> > > > > 	a group using the
> > > > > 	legacy interface, a modern driver can intercept
> > > > > 	the access and forward it to the owner device.
> > > > >
> > > > I will not mention "modern driver" as it has zero reference in
> > > > spec and don't
> > > want to bring Linux terms here.
> > > > "the driver can intercept" is enough.
> 
> Maybe a (non legacy) driver can intercept? Would that be acceptable?
> Just to clarify the confusion above.
> 
Non legacy driver wording is fine.

> > >  	when a legacy member device driver accesses a member device of
> > >  	a group using the
> > >  	legacy interface, an owner device driver can intercept
> > >  	the access and forward it to the owner device.
> > >
> > Above is not correct.
> >
> > We have 3 drivers in picture.
> > 1. guest driver
> 
> this is legacy driver, so easy
> 
> > 2. hypervisor level member device driver
> 
> this is just for notifications, optionally, yes?
> 
For notifications (optionally) and for configuration region access.

> 
> > 3. group owner device driver
> >
> > Trying to write without introducing guest and hypervisor term,
> >
> > A group owner device driver provides the service to access member device's
> configuration region.
> > A member device driver avail this service when it wants to access the member
> device's configuration region.
> 
> 
> I agree, it's getting complicated.
>
> >
> > > > I will rewrite it as,
> > > >
> > > > The group owner device should not expose PCI BAR0 in the PCI
> > > > SR-IOV extended capability for the group member PCI VF devices
> > > > when it prefers to
> > > support legacy interface for legacy configuration access using this group
> owner.
> > >
> > >
> > > This seems to ignore all my comments.
> > >
> > I replied after that, probably missed in exchanges.
> >
> > How about:
> > The group owner device MUST hardwire PCI BAR0 in the PCI SR-IOV extended
> capability for the group member PCI VF devices when it supports legacy
> configuration access commands.
> >
> 
> better but it's not a PCI BAR0. let's add link to sriov spec, and name it VF BAR0
> same as in that spec.
>
Yes, VF BAR0, will correct it.