[virtio-dev] RE: [virtio-comment] Re: [PATCH 09/11] transport-pci: Describe PCI MMR dev config registers

Parav Pandit
2023-04-12T05:01:34Z

> From: Jason Wang <jasowang@redhat.com>
> Sent: Wednesday, April 12, 2023 12:51 AM
>
> Yes, but this proposal will drag us back to legacy, isn't it?
No. This proposal supports the legacy transitional pci device.

> Or if it is used only in
> the vitalization environment, what's the advantages of doing it over simply
> mediating on top of modern device?
>
Because the spec for modern device do not allow it. Discussed in these threads.

> 1) legacy MMIO bar: spec changes, hypervisor mediation
> 2) modern device: no spec changes, hypervisor mediation
>
This question repeats the same discussion occurred in this patch series.
You might want to refer it again to avoid repeating all over again.

> 1) it's better not invent any of new facilities for legacy
> 2) if legacy is insisted, allow MMIO BAR0 is much simpler and better
You have missed few emails. :)
MMIO BAR is proposed here and it is not limited to BAR 0.
It is left for the device to either map something in existing BAR or use BAR 0.
Because PCI has only 3 BARs.
A device may want to support legacy and non-legacy functionality both at the same time.
So better not to hard wire for BAR 0.