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

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Date:	Thu, 20 Mar 2014 04:28:20 +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 11:31:31 PM Rafael J. Wysocki wrote:
> 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>

To speed up things a bit I changed the name of the new callback to ->stop_cpu
and made it void.

I also modified patch [2/2] accordingly and queued the both of them up for 3.15.

Please check the bleeding-edge branch.

I wouldn't like to need to do anything like that any more in the future, though.

> > ---
> >  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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