[virtio-dev] Re: [PATCH v10 4/4] transport-pci: Introduce group legacy group member config region access

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Jul 06, 2023 at 08:35:37PM +0000, Parav Pandit wrote:
> 
> > From: Michael S. Tsirkin <mst@redhat.com>
> > Sent: Thursday, July 6, 2023 4:29 PM
> > 
> > The driver has a final decision. Let's make it a SHOULD and then if driver knows
> > best then it has the choice?
> >
> 
> As you said, the driver has the final say.
> There is really no reason to complicate the spec for a narrow case where device cannot judge.
> 
> > 
> > > > But I don't see any configs where leaving this to the driver's
> > > > discretion is preferable. If you see one let me know.
> > >
> > > In doesn't need to be config.
> > > It is the environment that chooses which is preferred by the driver.
> > > For example preference of accessibility over ordering.
> > 
> > 
> > what does accessibility mean exactly? I definitely see OSes where owner driver
> > can't access a member.
> Accessibility = access a member
> 
> > So in that case naturally driver will skip the entry for member even if it's first.
> > maybe there are configs where member access is possible but is very slow e.g.
> > with lots of indirect function calls?
> > OK fine, but then it will be up to the driver to test and make damn sure the
> > benefits outweight the costs.
> > 
> > IOW it's a hint for the driver. If you like you can say it explicitly even.
> > 
> Device doesnt know anything about those indirect function calls, so device cannot hint about driver environment.
> 
> Can we please avoid this over engineering?
> Interface has the doors open for driver to make wise decision depending on its environment.

what if driver can access both with the same ease? this is the
case that bothers me and I think it's practical since it will be
common on linux.

-- 
MST


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