Re: [PATCH RFC] virtio-pci: add MMIO property

[Avi Kivity <avi@redhat.com>]

On 03/19/2012 05:56 PM, Michael S. Tsirkin wrote:
> Currently virtio-pci is specified so that configuration of the device is
> done through a PCI IO space (via BAR 0 of the virtual PCI device).
> However, Linux guests happen to use ioread/iowrite/iomap primitives
> for access, and these work uniformly across memory/io BARs.
>
> While PCI IO accesses are faster than MMIO on x86 kvm,
> MMIO might be helpful on other systems which don't
> implement PIO or where PIO is slower than MMIO.
>
> Add a property to make it possible to tweak the BAR type.
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>
> This is harmless by default but causes segfaults in memory.c
> when enabled. Thus an RFC until I figure out what's wrong.
>

Should be done via an extra BAR (with the same layout, perhaps extended)
so compatibility is preserved.

-- 
error compiling committee.c: too many arguments to function