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Re: [PATCH 09/10] cpuidle: declare cpuidle_dev in cpuidle.h

To: Daniel Lezcano <daniel.lezcano@linaro.org>
Subject: Re: [PATCH 09/10] cpuidle: declare cpuidle_dev in cpuidle.h
From: Paul Burton <paul.burton@imgtec.com>
Date: Thu, 20 Feb 2014 13:41:20 +0000
Cc: <linux-mips@linux-mips.org>, "Rafael J. Wysocki" <rjw@rjwysocki.net>, <linux-pm@vger.kernel.org>
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On Thu, Feb 20, 2014 at 02:35:18PM +0100, Daniel Lezcano wrote:
> On 01/15/2014 02:55 PM, Paul Burton wrote:
> >Declaring this allows drivers which need to initialise each struct
> >cpuidle_device at initialisation time to make use of the structures
> >already defined in cpuidle.c, rather than having to wastefully define
> >their own.
> >
> >Signed-off-by: Paul Burton <paul.burton@imgtec.com>
> >Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
> >Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
> >Cc: linux-pm@vger.kernel.org
> >---
> >  include/linux/cpuidle.h | 1 +
> >  1 file changed, 1 insertion(+)
> >
> >diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> >index 50fcbb0..bab4f33 100644
> >--- a/include/linux/cpuidle.h
> >+++ b/include/linux/cpuidle.h
> >@@ -84,6 +84,7 @@ struct cpuidle_device {
> >  };
> >
> >  DECLARE_PER_CPU(struct cpuidle_device *, cpuidle_devices);
> >+DECLARE_PER_CPU(struct cpuidle_device, cpuidle_dev);
> 
> 
> Nak. When a device is registered, it is assigned to the cpuidle_devices
> pointer and the backend driver should use it.
> 

Yes, but then if the driver needs to initialise the coupled_cpus mask
then it cannot do so until after the device has been registered. During
registration the cpuidle_coupled_register_device will then see the empty
coupled_cpus mask & do nothing. The only other ways around this would be
for the driver to define its own per-cpu struct cpuidle_device (which as
I state in the commit message seems wasteful when cpuidle already
defined them), or for cpuidle_coupled_register_device to be called later
after the driver had a chance to modify devices via the cpuidle_devices
pointers.

Paul

> 
> 
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