RE: [virtio-comment] Re: [PATCH 00/11] Introduce transitional mmr pci device

[Parav Pandit <parav@nvidia.com>]

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Wednesday, April 12, 2023 1:24 AM

> You are writing into modern register here. *what* are you writing there?
> with modern register the format depends on features. here you did not
> negotiate any features. 
Q notify content.

> what if NOTIFICATION_DATA is a required feature?
How can it be required when it is not defined in the legacy spec.

> with legacy there's no FEATURES_OK so no way to report failure.  driver barrels
> on, sends wrong data in the kick and hangs.
>
There is no need for FEATURE_OK because as 1.x configuration registers are not touched.

The device provide q notify register region for forwarding.

> 
> Look I know proposed this originally. I thought it's a small thing too.
> It was an idea. I am not sure it pans out though. Not all ideas work.

This one do work and we have been already testing it.
Described changes with modern devices are simpler than the original proposal indeed.