Re: [RFC] virtio-mmio: Update the device to OASIS spec version

[Pawel Moll <pawel.moll@arm.com>]

On Mon, 2015-01-19 at 18:36 +0000, Michael S. Tsirkin wrote:
> > > > Well, not quite: as of now I've got legacy block device driver happily
> > > > working on top of compliant (so v2 in MMIO speech) MMIO device - the
> > > > transport if completely transparent here.
> > > 
> > > Spec says explicitly it's an illegal configuration.
> > 
> > What part of the spec exactly? The closest I can think of are 2.2.3, 6.2
> > and 6.3. Both legacy and spec-complaint MMIO transports will satisfy all
> > requirements from those paragraphs, whether VIRTIO_F_VERSION_1 is
> > negotiated or not.
> 
> The parts that say VIRTIO_F_VERSION_1 MUST be set.
> I'll look up the chapter and verse later if you like.

That would be:

"6.1 Driver Requirements: Reserved Feature Bits
A driver MUST accept VIRTIO_F_VERSION_1 if it is offered. A driver MAY
fail to operate further if VIRTIO_F_VERSION_1 is not offered."

"6.2 Device Requirements: Reserved Feature Bits
A device MUST offer VIRTIO_F_VERSION_1. A device MAY fail to operate
further if VIRTIO_F_VERSION_1 is not accepted."

Both are perfectly clear and reasonable for me. And the MMIO transport
in both versions (pre-spec and the spec one) will meet those
requirements, as it was able to pass more than 32 features bits from the
very beginning.

> Can you please also add a comment?
> E.g. 
>      /*
>       * MMIO uses ID 0 to mean device not present.  Avoid probing
>       * the device further: it's sure to fail anyway.
>       */

There is a comment:

> On Fri, 2014-12-19 at 18:38 +0000, Pawel Moll wrote: 
> > +		/*
> > +		 * ID 0 means a dummy (placeholder) device, skip quietly
> > +		 * (as in: no error) with no further actions
> > +		 */
> 
But I'm can use your wording if you find it better.

Pawel