linux-kernel - Re: [PATCH v2 1/2] cpufreq: Add exit_prepare callback to cpufreq

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Date:	Sat, 15 Mar 2014 03:04:55 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	dirk.brandewie@...il.com
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	patrick.marlier@...il.com,
	Dirk Brandewie <dirk.j.brandewie@...el.com>
Subject: Re: [PATCH v2 1/2] cpufreq: Add exit_prepare callback to cpufreq_driver interface

On Friday, March 14, 2014 02:03:56 PM dirk.brandewie@...il.com wrote:
> From: Dirk Brandewie <dirk.j.brandewie@...el.com>
> 
> This callback allows the driver to do clean up before the CPU is
> completely down and its state cannot be modified.  This is used
> by the intel_pstate driver to reduce the requested P state prior to
> the core going away.  This is required because the requested P state
> of the offline core is used to select the package P state. This
> effectively sets the floor package P state to the requested P state on
> the offline core.
> 
> Signed-off-by: Dirk Brandewie <dirk.j.brandewie@...el.com>
> ---
>  Documentation/cpu-freq/cpu-drivers.txt | 8 +++++++-
>  drivers/cpufreq/cpufreq.c              | 3 +++
>  include/linux/cpufreq.h                | 1 +
>  3 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/cpu-freq/cpu-drivers.txt b/Documentation/cpu-freq/cpu-drivers.txt
> index 8b1a445..79def80 100644
> --- a/Documentation/cpu-freq/cpu-drivers.txt
> +++ b/Documentation/cpu-freq/cpu-drivers.txt
> @@ -61,7 +61,13 @@ target_index		-	See below on the differences.
>  
>  And optionally
>  
> -cpufreq_driver.exit -		A pointer to a per-CPU cleanup function.
> +cpufreq_driver.exit -		A pointer to a per-CPU cleanup
> +		    		function called during CPU_POST_DEAD
> +		    		phase of cpu hotplug process.
> +
> +cpufreq_driver.stop -		A pointer to a per-CPU stop function
> +			    	called during CPU_DOWN_PREPARE phase of
> +				cpu hotplug process.
>  
>  cpufreq_driver.resume -		A pointer to a per-CPU resume function
>  				which is called with interrupts disabled
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index cf485d9..0d430d7 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1338,6 +1338,9 @@ static int __cpufreq_remove_dev_prepare(struct device *dev,
>  		}
>  	}
>  
> +	if (cpufreq_driver->stop)

What about doing

+	if (cpufreq_driver->setpolicy && cpufreq_driver->stop)

here instead?  That would make it clear where the new callback belongs.

If you're fine with that, I can make that change when applying the patch.

> +		cpufreq_driver->stop(policy);
> +
>  	return 0;
>  }
>  
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index 4d89e0e..ff8db19 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -224,6 +224,7 @@ struct cpufreq_driver {
>  	int	(*bios_limit)	(int cpu, unsigned int *limit);
>  
>  	int	(*exit)		(struct cpufreq_policy *policy);
> +	int	(*stop)		(struct cpufreq_policy *policy);
>  	int	(*suspend)	(struct cpufreq_policy *policy);
>  	int	(*resume)	(struct cpufreq_policy *policy);
>  	struct freq_attr	**attr;
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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