linux-kernel - Re: [PATCH 2/3] devfreq: Add suspend and resume apis

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Date:	Mon, 10 Sep 2012 09:27:56 +0000 (GMT)
From:	MyungJoo Ham <myungjoo.ham@...sung.com>
To:	Rajagopal Venkat <rajagopal.venkat@...aro.org>,
	"mturquette@...aro.org" <mturquette@...aro.org>,
	박경민 <kyungmin.park@...sung.com>,
	"rjw@...k.pl" <rjw@...k.pl>
Cc:	"patches@...aro.org" <patches@...aro.org>,
	"linaro-dev@...ts.linaro.org" <linaro-dev@...ts.linaro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] devfreq: Add suspend and resume apis

> Add devfreq suspend/resume apis for devfreq users. This patch
> supports suspend and resume of devfreq load monitoring, required
> for devices which can idle.
> 
> Signed-off-by: Rajagopal Venkat <rajagopal.venkat@...aro.org>

Rather than letting device driver be responsible to call devfreq_suspend_device() or devfreq_dev_suspend(),would there be any problems in using pm notifier here? (calling the event handler with DEVFREQ_GOV_SUSPEND/RESUME at pm notifier, stopping them earlier and resuming tham later)

What devfreq-core and devfreq-governors do with suspend/resume is handling the delayed workqueue and it does not have anything to do with device-specific tasks. Thus, having each device driver handle device-specifics with its own pm_ops and having devfreq-core stop sampling seem appropriate.

Putting another burden to each device driver (to call devfreq_suspend/resume_device() at its pm_ops) for an obvious task that could be done at core doesn't seem fair.

Thank you.



Cheers!
MyungJoo

> ---
>  drivers/devfreq/devfreq.c                 | 26 ++++++++++++++++++++++++++
>  drivers/devfreq/governor.h                |  2 ++
>  drivers/devfreq/governor_simpleondemand.c |  9 +++++++++
>  include/linux/devfreq.h                   | 12 ++++++++++++
>  4 files changed, 49 insertions(+)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index be524c7..3a5f126 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -365,6 +365,32 @@ int devfreq_remove_device(struct devfreq *devfreq)
>  }
>  EXPORT_SYMBOL(devfreq_remove_device);
>  
> +/**
> + * devfreq_suspend_device() - Suspend devfreq of a device.
> + * @devfreq	the devfreq instance to be suspended
> + */
> +int devfreq_suspend_device(struct devfreq *devfreq)
> +{
> +	if (!devfreq)
> +		return -EINVAL;
> +
> +	return devfreq->governor->event_handler(devfreq, DEVFREQ_GOV_SUSPEND);
> +}
> +EXPORT_SYMBOL(devfreq_suspend_device);
> +
> +/**
> + * devfreq_resume_device() - Resume devfreq of a device.
> + * @devfreq	the devfreq instance to be resumed
> + */
> +int devfreq_resume_device(struct devfreq *devfreq)
> +{
> +	if (!devfreq)
> +		return -EINVAL;
> +
> +	return devfreq->governor->event_handler(devfreq, DEVFREQ_GOV_RESUME);
> +}
> +EXPORT_SYMBOL(devfreq_resume_device);
> +
>  static ssize_t show_governor(struct device *dev,
>  			     struct device_attribute *attr, char *buf)
>  {
> diff --git a/drivers/devfreq/governor.h b/drivers/devfreq/governor.h
> index 4a86af7..7dbbdfc 100644
> --- a/drivers/devfreq/governor.h
> +++ b/drivers/devfreq/governor.h
> @@ -22,6 +22,8 @@
>  #define DEVFREQ_GOV_START			0x1
>  #define DEVFREQ_GOV_STOP			0x2
>  #define DEVFREQ_GOV_INTERVAL			0x3
> +#define DEVFREQ_GOV_SUSPEND			0x4
> +#define DEVFREQ_GOV_RESUME			0x5
>  
>  /* Caution: devfreq->lock must be locked before calling update_devfreq */
>  extern int update_devfreq(struct devfreq *devfreq);
> diff --git a/drivers/devfreq/governor_simpleondemand.c b/drivers/devfreq/governor_simpleondemand.c
> index 9802bf9..35b8e8e 100644
> --- a/drivers/devfreq/governor_simpleondemand.c
> +++ b/drivers/devfreq/governor_simpleondemand.c
> @@ -113,6 +113,15 @@ int devfreq_simple_ondemand_handler(struct devfreq *devfreq,
>  		else
>  			ret = devfreq_monitor_resume(devfreq);
>  		break;
> +
> +	case DEVFREQ_GOV_SUSPEND:
> +		ret = devfreq_monitor_suspend(devfreq);
> +		break;
> +
> +	case DEVFREQ_GOV_RESUME:
> +		ret = devfreq_monitor_resume(devfreq);
> +		break;
> +
>  	default:
>  		break;
>  	}
> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
> index 7a11c3e..7c7e179 100644
> --- a/include/linux/devfreq.h
> +++ b/include/linux/devfreq.h
> @@ -155,6 +155,8 @@ extern struct devfreq *devfreq_add_device(struct device *dev,
>  				  const struct devfreq_governor *governor,
>  				  void *data);
>  extern int devfreq_remove_device(struct devfreq *devfreq);
> +extern int devfreq_suspend_device(struct devfreq *devfreq);
> +extern int devfreq_resume_device(struct devfreq *devfreq);
>  
>  /* Helper functions for devfreq user device driver with OPP. */
>  extern struct opp *devfreq_recommended_opp(struct device *dev,
> @@ -208,6 +210,16 @@ static int devfreq_remove_device(struct devfreq *devfreq)
>  	return 0;
>  }
>  
> +static int devfreq_suspend_device(struct devfreq *devfreq)
> +{
> +	return 0;
> +}
> +
> +static int devfreq_resume_device(struct devfreq *devfreq)
> +{
> +	return 0;
> +}
> +
>  static struct opp *devfreq_recommended_opp(struct device *dev,
>  					   unsigned long *freq, u32 flags)
>  {
> -- 
> 1.7.11.3
> 
> 
> 
> 
>        
>   
>          
>