RE: [virtio-comment] Re: [PATCH 0/2] Selective queue enabling

[Parav Pandit <parav@nvidia.com>]

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Tuesday, June 13, 2023 5:48 PM

> > Why queue_reset is needed here?
> > I don't see spec saying that queue_enable must be done only once for a given
> Q before DRIVER_OK.
> 
> I see you found it.
> 
> > > - program another queue address, size
> > >
> > > Finally we are decided, let's start operating:
> > >
> > > - DRIVER_OK
> > >
> > >
> > > I don't see how it's possible with just queue_enable.
> > >
> > >
> > > >
> > > > It is not explicitly mentioned in the spec that one can setup the
> > > > queue using
> > > queue reset instead of queue enable.
> > > > As Jason mentioned it is implementation specific, one device
> > > > supports it and
> > > one doesn't.
> > > > Hence, it will break on those devices which doesnt support it.
> > > >
> > >
> > > Setup? No, and spec explicitly says to setup one has to use
> > > queue_enable. But this is not what we discussed with Stefano here.
> > >
> > The above sequence you described is not well documented.
> 
> It's the standard sequence for queue reset, is it not?
> 
> For example:
> 
> 	Virtqueue reset is divided into two parts. The driver first resets a queue
> and
> 	can afterwards optionally re-enable it.
> 
> 
> it seems clear that queue has to be enabled before being reset.
>
Yes, it is clear.
 
> I'm not sure what's broken.
>
If a device has assumed that queue_reset must be done after DRIVER_OK stage because until that point the device is not "live",
Such device needs the fix.