Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO BAR

[David Gibson]

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<address@hidden>
> 
> 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