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Subject: Re: [PATCH 2/4]: CPUIDLE: Introduce architecture independent
 cpuidle_pm_idle in drivers/cpuidle/cpuidle.c
From: Peter Zijlstra <peterz@infradead.org>
To: arun@linux.vnet.ibm.com
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       Joel Schopp <jschopp@austin.ibm.com>, Paul Mackerras <paulus@samba.org>,
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Date: Fri, 28 Aug 2009 09:01:12 +0200
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On Fri, 2009-08-28 at 08:48 +0200, Peter Zijlstra wrote:
> 
> > void cpuidle_install_idle_handler(void)
> > {
> >       .........
> >       .........
> >       cpuidle_pm_idle = cpuidle_idle_call;
> > }
> 
> All I'm seeing here is a frigging mess.
> 
> How on earths can something called: cpuidle_install_idle_handler() have
> a void argument, _WHAT_ handler is it going to install?

Argh, now I see, it installs itself as the platform idle handler.

so cpuidle_install_idle_handler() pokes at the unmanaged pm_idle pointer
to make cpuidle take control.

On module load it does:

 pm_idle_old = pm_idle;

then in the actual idle loop it does:

        if (!dev || !dev->enabled) {
                if (pm_idle_old)
                        pm_idle_old();

who is to say that the pointer stored at module init time is still
around at that time?

So cpuidle recognised the pm_idle stuff was a flaky, but instead of
fixing it, they build a whole new layer on top of it. Brilliant.

/me goes mark this whole thread read, I've got enough things to do.