Re: [virtio-comment] Re: [PATCH v6 2/5] virtio-net: Add flow filter capabilities read commands

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

On Fri, Nov 24, 2023 at 06:31:03AM +0000, Parav Pandit wrote:
> 
> > From: Michael S. Tsirkin <mst@redhat.com>
> > Sent: Friday, November 24, 2023 11:48 AM
> > 
> > On Fri, Nov 24, 2023 at 05:40:26AM +0000, Parav Pandit wrote:
> > > > we
> > > > strongly suggest that *drivers* support both old and new mechanism,
> > > > and then *devices* will only implement what's required.
> > > There are other examples in the same document that makes things worst
> > with old and new.
> > >
> > > Also there is literally no way to enforce that driver supports both
> > > and new. It is just sounds like an excuse to force infinite config
> > > space.
> > 
> > There is a very simple method though.  We allow devices to expose a subset of
> > features when DMA is not used. So drivers that want maximum features will
> > always opt for DMA. We can also strongly recommend that all drivers support
> > DMA if available.
> Yeah, don't see how this is elegant at all with all mixed bits.

It's elegant because simple low end devices can cheaply implement MMIO
and not worry about DMA.

> Nor do I see any enforcement, single method via cvq still holds strong.

You don't need to enforce things, if people want to put a lot of
RAM on device and put it in a register let them.

> 
> > 
> > 
> > 
> > > The method proposed here is elegant and clearly promote one way to do
> > things for driver and device with predictability.
> > >
> > 
> > I don't see it as elegant at all. What is elegant is *a single tag* that describes
> > each property of the device. And this single tag should be good for everything:
> > driver, provisioning, migration. And config space offset serves as such.
> The single tag is the set of structures.

I have no idea how this will work. If migration format i started
reviewing is anything to go by then there will be a huge elaborate
structure nothing single or simple. By comparison there's already
a proposal how provisioning can work by supplying config space.
it is just a clean model to grasp.

> Provisioning access them via owner device.
> Member driver access them via CVQ or 1.2 legacy config space.


-- 
MST