CPU hotplug vs. cpufreq on ppc64

[Johannes Berg]

I'm having an odd problem with ppc64 cpufreq and cpu hotplug. The cpu
hotplug I'm doing is just fake, but I need to unplug the CPUs for
suspend.

When the system boots up, all CPUs are added as such:
[   18.132830] cpufreq-core: trying to register driver powermac
[   18.132835] cpufreq-core: adding CPU 0
[   18.132976] cpufreq-core: CPU 1 already managed, adding link
[   18.132983] cpufreq-core: CPU 2 already managed, adding link
[   18.132989] cpufreq-core: CPU 3 already managed, adding link
[   18.132998] cpufreq-core: setting new policy for CPU 0: 1250000 - 2500000 kHz
[   18.133025] cpufreq-core: new min and max freqs are 1250000 - 2500000 kHz
[   18.133029] cpufreq-core: governor switch
[   18.133033] cpufreq-core: __cpufreq_governor for CPU 0, event 1
[   18.133043] cpufreq-core: target for CPU 0: 2500000 kHz, relation 1
[   18.133056] cpufreq-core: governor: change or update limits
[   18.133060] cpufreq-core: __cpufreq_governor for CPU 0, event 3
[   18.133069] cpufreq-core: target for CPU 0: 2500000 kHz, relation 1
[   18.133082] cpufreq-core: initialization complete
[   18.133086] cpufreq-core: adding CPU 1
[   18.133089] cpufreq-core: adding CPU 2
[   18.133092] cpufreq-core: adding CPU 3
[   18.133097] cpufreq-core: driver powermac up and running

This says that the 4 CPUs can actually only be switched all together
with CPU0. This is achieved by doing

        policy->cpus = cpu_possible_map;
in
g5_cpufreq_cpu_init (arch/powerpc/platforms/powermac/cpufreq_64.c)


When I suspend now, I get
[  167.563428] cpufreq-core: unregistering CPU 1
[  167.563440] cpufreq-core: removing link
[  167.569139] cpufreq-core: target for CPU 0: 1250000 kHz, relation 1
[  167.573690] cpufreq-core: unregistering CPU 2
[  167.573704] cpufreq-core: removing link
[  167.576175] cpufreq-core: target for CPU 0: 1250000 kHz, relation 1
[  167.582261] cpufreq-core: unregistering CPU 3
[  167.582270] cpufreq-core: removing link
[  168.415156] cpufreq-core: suspending cpu 0
[  168.415164] cpufreq-core: suspending cpu 1
[  168.415170] cpufreq-core: suspending cpu 2
[  168.415177] cpufreq-core: suspending cpu 3

which seems fine. However, when I resume, I get
[  168.446692] cpufreq-core: resuming cpu 0
[  168.446708] cpufreq-core: resuming cpu 1
[  168.446715] cpufreq-core: resuming cpu 2
[  168.446721] cpufreq-core: resuming cpu 3
[  168.624880] cpufreq-core: handle_update for cpu 0 called
[  168.624893] cpufreq-core: updating policy for CPU 0
[  168.624905] cpufreq-core: setting new policy for CPU 0: 1250000 - 2500000 kHz
[  168.624965] cpufreq-core: new min and max freqs are 1250000 - 2500000 kHz
[  168.624974] cpufreq-core: governor: change or update limits
[  168.624982] cpufreq-core: __cpufreq_governor for CPU 0, event 3
[  168.625009] cpufreq-core: target for CPU 0: 1250000 kHz, relation 0
[  169.232726] cpufreq-core: adding CPU 1
[  169.232741] cpufreq-core: initialization failed
[  169.239623] cpufreq-core: adding CPU 2
[  169.239636] cpufreq-core: initialization failed
[  169.247240] cpufreq-core: adding CPU 3
[  169.247255] cpufreq-core: initialization failed

The question now is where this needs to be handled, and how. The driver
can't really say that it initialised fine because it's still initialised
on CPU0. However, I suppose that for real CPU hotplug cpufreq can't try
to remember the pre-unplug groups either...

johannes
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