linux-kernel - Re: [PATCH 10/16] cpuidle: pseries: Convert to hotplug state machine

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Message-ID: <20160823163206.xe7dg7ulzj4pzzrs@linutronix.de>
Date:   Tue, 23 Aug 2016 18:32:06 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, rt@...utronix.de,
        "Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org
Subject: Re: [PATCH 10/16] cpuidle: pseries: Convert to hotplug state machine

On 2016-08-23 16:16:12 [+0200], Daniel Lezcano wrote:
> Yes. If we can limit the number of duplicating enum for the same purpose
> right now, it would be nice.
Okay.

> > We could do that but you would have to ensure that only one CPUIDLE
> > driver registers itself at a time and for those powerpc drivers it looks
> > like you could have two registered (not sure about ARM's little/big (if
> > you could have two of those later at run-time)).
> 
> At the first glance, I don't think it is possible to register the cpu
> hotplug callback twice because the cpuidle drivers are doing:
…
> So if a previous driver was already registered, cpuidle_register will
> fail and register_cpu_notifier won't be hit.
> 
> There is the same scenario for intel_idle and processor_idle (acpi).

I tried to preserve everything as-is during the conversation. However if
you are explicitly asking for this and you are sure that it will work
then you can get it. No problem :)

Sebastian