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 3:43 PM
> 
> On Wed, Jun 21, 2023 at 04:01:00PM +0000, Parav Pandit wrote:
> >
> >
> > > From: Michael S. Tsirkin <mst@redhat.com>
> > > Sent: Wednesday, June 21, 2023 11:56 AM
> >
> > > Not like v3 please. If you want to re-open this:
> > >
> > >
> > > First I think we need multiple offsets just like notification
> > > capaiblity, sorted by priority. Second I think we need ability to
> > > report offset within owner not member.
> > >
> > > So please add ability to report multiple offsets, and add e.g.
> > > a flags field, with bits for owner, member.
> >
> > What are these multiple offsets for?
> 
> Different BARs.  For example, IO versus memory. Yes I know VFs don't support
> IO but PFs do. prefetch vs non-prefetch might matter too (non-prefetch is
> mostly limited to 32 bit).
>
BAR type and its prefetch attributes are told by the PCI anyway so no duplication here anyway.
For owner and member I get it. 
> 
> > Do you mean two offsets? One for owner and one for member?
> > Both bits are optional. Do you agree?
> 
> I agree that everything should be optional sure. Let's not limit it to two though.
> There could be multiple BARs or whatever. We have ability to pass buffers of
> arbitrary length and device reports the length.
> Maybe have a SHOULD recommending not more than 10 of these (1 for each
> possible PCI BAR one for each possible VF BAR).
> 
> This is to match the functionality that notification capability has.
> 
A device can expose multiple offsets within the single bar to a count of 100 entries;
Also allowed in the notification capability.
(I don't see why any sane device would do that anyway)

So I will avoid such extra restrictions and limit the scope of this patch to be minimal to have arbitrary number of BAR entries limited by the command result length.

> 
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