Re: [Qemu-devel] [PATCH RFC] vga: flag vga ram for notifiers

[Michael S. Tsirkin]

On Thu, Mar 31, 2011 at 04:49:46PM -0500, Anthony Liguori wrote:
> On 03/31/2011 04:38 PM, Michael S. Tsirkin wrote:
> >
> >>That seems like a clearer API, yes. I think it makes it much more
> >>obvious what it's trying to achieve.
> >>
> >>-- PMM
> >Maybe register_dma_area - its' not 100% virtio specific.
> 
> It's never been clear to me whether that's true or not.  I've heard
> mixed things about whether devices DMA to other devices.  I've never
> been able to find something in a specification stating
> authoritatively one way or another.
> 
> Regards,
> 
> Anthony Liguori
> 

AFAIK the capability of cross-talk between PCI devices
exists in PCI and is optional in PCI Express.

PCI spec says:
        Full multi-master capability allowing any PCI master peer-to-peer
        access to any PCI master/target.

The Express spec says:
        "The capability to route peer-to-peer transactions between hierarchy
        domains through a Root Complex is optional and implementation dependent.
        For example, an implementation may incorporate a real or virtual Switch
        internally within the Root Complex to enable full peer-to- peer support
        in a software transparent way."

However I don't think guests use this with devices we emulate in any way.

Haven't looked at ISA.

-- 
MST