[PATCH] powermac: support G5 CPU hotplug

[Paul Mackerras]

Johannes Berg writes:

> This patch allows "hotplugging" of CPUs on G5 machines. CPUs that are
> disabled are put into an idle loop with the decrementer frequency set
> to minimum. To wake them up again we kick them just like when bringing
> them up. To stop those CPUs from messing with any global state we stop
> them from entering the timer interrupt.

Ultimately we want to put the disabled cpus in sleep mode, but that
will require a suitable cache flush routine.

For now, the patch mostly looks OK, except that I would prefer that
you make power4_idle_irqs_softdisabled a separate function from
power4_idle (and choose a better name while you're there :).  There
are enough differences between power4_idle and your new routine that
it would be clearer if they're separate.  For one thing your new
routine wouldn't need to set _TLF_NAPPING, for another, it wouldn't
need the conditional branch at the end.  Also you could do the test
for the nap capability in the caller.

Paul.