Re: [Qemu-devel] [RFC PATCH 03/26] target/ppc/POWER9: add POWERPC_EXCP_POWER9

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Tue, 2017-07-11 at 15:52 +0200, Cédric Le Goater wrote:
> 
> > Just as we could build a POWER9 with XICS in qemu, we could build a 
> > POWER8 with XIVE.
> 
> That might be the case with a POWER9 running in POWER8 compat mode. 
> I need to check. 

Yes. In "compat" mode (or more generally if the guest doesn't advertize
support for native XIVE, whether it's in compat or native P9 mode is
irrelevant in fact), we provide the old hcalls and effectively need to
instantiate a XICS in qemu (KVM will exploit the XIVE under the hood
but will make it look like a XICS to qemu ioctl's as well).

Cheers,
Ben.

> Thanks,
> 
> C. 
> 
> 
> > > > > > Now.. I could imagine the POWER9 having a different core model that
> > > > > > came along with XIVE, but I can't see this new model being used for
> > > > > > anything anywhere in the rest of the series.
> > > > > 
> > > > > See patch 26. But, maybe, I am taking a shortcut and we need another
> > > > > family of flags. 
> > > > 
> > > > Or just some kind of enum for the interrupt controller, how do we do
> > > > with OpenPIC vs. XICS already ? Old POWER3 had OpenPIC.
> > > 
> > > AFAICT, we don't have such a CPU in QEMU/ppc.
> > 
> > More to the point we don't have any machine type for those old POWER3
> > setups.
> > 
> > > We could use some extra flag to change the ICS behavior. The path I am
> > > taking duplicates the ICS code but in real, we only need to change the
> > > irq handlers. 
> > > 
> > > Thanks,
> > > 
> > > C. 
> > >