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

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Date:	Wed, 19 Mar 2014 23:31:31 +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, viresh.kumar@...aro.org,
	srivatsa.bhat@...ux.vnet.ibm.com,
	Dirk Brandewie <dirk.j.brandewie@...el.com>
Subject: Re: [PATCH 1/2] cpufreq: Add stop callback to cpufreq_driver interface

On Wednesday, March 19, 2014 08:45:53 AM 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, 10 insertions(+), 2 deletions(-)
> 
> 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..bb20292 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1336,7 +1336,8 @@ static int __cpufreq_remove_dev_prepare(struct device *dev,
>  						__func__, new_cpu, cpu);
>  			}
>  		}
> -	}
> +	} else if (cpufreq_driver->stop && cpufreq_driver->setpolicy)
> +		cpufreq_driver->stop(policy);

Nit: Why is it an int function if the only caller doesn't check the
return value?  It should be void.

>  
>  	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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