Re: [virtio] [PATCH 3/3] VIRTIO-110: ARM's feedback for MMIO chapter, clarifications

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

On Tue, 2014-08-05 at 13:04 +0100, Michael S. Tsirkin wrote:
> > > > +The driver MAY use other accesses for the device-specific configuration space,
> > > > +depending on the device type.
> > > 
> > > Why are you adding this option?
> > > If there's a 4 byte register it is a pain for devices to support
> > > 1 byte accesses, and we gain nothing from it.
> > 
> > But 2.3 does not limit the configuration space field size nor alignment,
> > does it?
> 
> No but there is no need: you look at each specific field, you see what
> the size and alignment is.

That's what I'm saying. The driver MAY do 8-bit load of the 8-bit field,
if the field is defined as such in the device spec. Otherwise all
operations on the configuration space would have to be 32-bit wide and
aligned. We don't want this, do we? (or do we? :-)

> Are you supporting transitional devices for MMIO?
> If no you don't care what happens with existing drivers.

I don't indeed.

Paweł