Re: [Qemu-ppc] [RFC PATCH v2 13/21] ppc/xive: handle interrupt acknowledgment by the O/S

[Benjamin Herrenschmidt]

On Wed, 2017-09-20 at 11:40 +0200, Cédric Le Goater wrote:
> > Plus, this doesn't seem right.  Shouldn't this
> > recheck the CPPR against the PIPR, in case a higher priority irq has
> > been delivered since the one the cpu is acking.
> 
> If a higher priority is delivered, it means that the CPPR was more 
> privileged and that we have now two bits set in the IPB by the time 
> the interrupt is acked. The high priority PIPR will become the new 
> CPPR and the IBP will be modified keeping only the lower priority. 
> 
> if the CPPR is modified to the lower priority level, then the 
> first interrupt will be delivered again. 
> 
> I think this is fine.

Also remember the HW PIPR behaviour, its a bit odd, it will be clamped
by the CPPR. So if CPPR is 0 PIPR will be 0.

If CPPR is 7, PIPR will be <= 7, etc...

Cheers,
Ben.