On Tue, Nov 01, 2011 at 05:20:06PM -0500, Anthony Liguori wrote:
> On 09/30/2011 12:26 AM, David Gibson wrote:
> >Currently, virtio devices are usually presented to the guest as an
> >emulated PCI device, virtio_pci. Although the actual IO operations
> >are done through system memory, the configuration of the virtio device
> >is done through the one PCI IO space BAR that virtio_pci presents.
> >
> >But PCI IO space (aka PIO) is deprecated for modern PCI devices, and
> >on some systems with many PCI domains accessing PIO space can be
> >problematic. For example on the existing PowerVM implementation of
> >the PAPR spec, PCI PIO access is not supported at all. We're hoping
> >that our KVM implementation will support PCI PIO (once we support PCI
> >at all), but it will probably have some irritating limitations.
> >
> >This patch, therefore, extends the virtio_pci device to have a PCI
> >memory space (MMIO) BAR as well as the IO BAR. The MMIO BAR contains
> >exactly the same registers, in exactly the same layout as the existing
> >PIO BAR.
> >
> >Because the PIO BAR is still present, existing guest drivers should
> >still work fine. With this change in place, future guest drivers can
> >check for an MMIO BAR and use that if present (falling back to PIO
> >when possible to support older qemu versions).
> >
> >Signed-off-by: David Gibson<da...@gibson.dropbear.id.au>
>
> Seems harmless for QEMU, so applied. You should update the
> virtio-pci spec too.
Ugh, sorry. This is the old version of the patch which breaks when
you actually use it because it attempts to give proxy->bar two
different parents. I have a new version which does it correctly.
So, do you want to revert and reapply, or should I just make a fix
patch?
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
