[PATCH v2] ARM: DT: Add binding for GIC virtualization extentions (VGIC)

[Arnd Bergmann]

On Wednesday 09 May 2012, Marc Zyngier wrote:
> > 
> > Sounds good. I don't have a strong preference whether that should be a
> > property like you suggest or a separate "compatible" value, maybe Rob or
> > Grant can comment on what they prefer.
> 
> At the moment, the compatible string should be pretty explicit, as it is
> not possible to build an A7 or A15 based SoC without the virtualization
> extensions.

Ok, makes sense. Then again, if you run an A15 guests on an A15 host,
the virtual GIC would not have those extensions, right?

> > On the guest side, is it guaranteed that the virtual GIC looks like
> > a real GIC without those extensions? If the actual behavior depends on
> > the hypervisor, it might still make sense to add another flag in there
> > to tell that it's virtual, even if we don't require it for now.
> 
> Nothing is really guaranteed, as the VGIC only exposes a GIC CPU interface
> to the guest, and the distributor has to be modeled by the hypervisor. But
> if the difference is observable by the guest, is it still a GIC? And how to
> differentiate between behavior A and behavior B with a single flag?

Right, in that case, we would probably want a hypervisor specific compatible
property to identify it.
 
> My take would be that if the guest can tell the difference, than it
> shouldn't be called a GIC, and have separate bindings. Or at least a
> different compatible string that we could use to enable quirks in the
> driver.

Ok, good.

	Arnd