Re: [RFC 1/4] PM / devfreq: Add DevFreq subsystem suspend/resume

[Chanwoo Choi <cw00.choi@samsung.com>]

Hi Tobias,

I like your suggestion. But I have some comment on below.

On 2016년 11월 23일 22:51, Tobias Jakobi wrote:
> This suspend/resume operations works analogous to the
> cpufreq_{suspend,resume}() calls in the CPUFreq subsystem.
> 
> Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
> ---
>  drivers/devfreq/devfreq.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/devfreq.h   | 10 +++++++
>  2 files changed, 85 insertions(+)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index bf3ea76..2f1aa83 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -785,6 +785,81 @@ int devfreq_resume_device(struct devfreq *devfreq)
>  EXPORT_SYMBOL(devfreq_resume_device);
>  
>  /**
> + * devfreq_suspend() - Suspend DevFreq governors
> + *
> + * Called during system wide Suspend/Hibernate cycles for suspending governors
> + * in the same fashion as cpufreq_suspend().
> + */
> +void devfreq_suspend(void)
> +{
> +	struct devfreq *devfreq;
> +	unsigned long freq;
> +	int ret;
> +
> +	mutex_lock(&devfreq_list_lock);
> +
> +	list_for_each_entry(devfreq, &devfreq_list, node) {
> +		if (!devfreq->suspend_freq)
> +			continue;
> +
> +		ret = devfreq_suspend_device(devfreq);
> +		if (ret < 0) {
> +			dev_warn(&devfreq->dev, "%s: governor suspend failed\n", __func__);
> +			continue;
> +		}
> +
> +		devfreq->resume_freq = 0;
> +		if (devfreq->profile->get_cur_freq) {
> +			ret = devfreq->profile->get_cur_freq(devfreq->dev.parent, &freq);
> +			if (ret >= 0)
> +				devfreq->resume_freq = freq;
> +		}
> +
> +		freq = devfreq->suspend_freq;
> +		ret = devfreq->profile->target(devfreq->dev.parent, &freq, 0);


DEVFREQ subsystem has the passive governor[2] and devfreq device using passive[1]
governor depends on the parent devfreq device. The passive governor uses
'DEVFREQ_TRANSITION_NOTIFIER' notifier to track the changed state of
parent devfreq device.

When changing the clock/voltage of parent devfreq device,
DEVFREQ subsystem have to notify the changed frequency
to the passive devfreq device.

So, you should call the devfreq_notifiy_transition()
before/after 'devfreq->profile->target' as following:
You can refer the update_devfreq() function 
that is how to use devfreq_notifiy_transition().

For example,
		struct devfreq_freq freqs;
 
		if (devfreq->profile->get_cur_freq) {
			ret = devfreq->profile->get_cur_freq(devfreq->dev.parent, &freq);
			if (ret >= 0)
				devfreq->resume_freq = freq;
		} else {
			devfreq->resume_freq = devfreq_previous_freq;
		} 

		freqs.old = devfreq->resume_freq;
		freqs.new = devfreq->suspend_freq;
		devfreq_notify_transition(devfreq, &freqs, DEVFREQ_PRECHANGE);

                freq = devfreq->suspend_freq;
                ret = devfreq->profile->target(devfreq->dev.parent, &freq, 0);
 
		freqs.new = freq;
		devfreq_notify_transition(devfreq, &freqs, DEVFREQ_POSTCHANGE);

                if (ret < 0)
                        dev_warn(&devfreq->dev, "%s: setting suspend frequency failed\n", __func__);
        }

[1] DEVFREQ_TRANSITION_NOTIFIER notifier
- https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=0fe3a66410a3ba96679be903f1e287d7a0a264a9
[2] DEVFREQ passive governor
- https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=996133119f57334c38b020dbfaaac5b5eb127e29

> +
> +		if (ret < 0)
> +			dev_warn(&devfreq->dev, "%s: setting suspend frequency failed\n", __func__);
> +	}
> +
> +	mutex_unlock(&devfreq_list_lock);
> +}
> +
> +/**
> + * devfreq_resume() - Resume DevFreq governors
> + *
> + * Called during system wide Suspend/Hibernate cycle for resuming governors that
> + * are suspended with devfreq_suspend().
> + */
> +void devfreq_resume(void)
> +{
> +	struct devfreq *devfreq;
> +	unsigned long freq;
> +	int ret;
> +
> +	mutex_lock(&devfreq_list_lock);
> +
> +	list_for_each_entry(devfreq, &devfreq_list, node) {
> +		if (!devfreq->suspend_freq)
> +			continue;
> +
> +		freq = devfreq->resume_freq;
> +		ret = devfreq->profile->target(devfreq->dev.parent, &freq, 0);

ditto.

> +
> +		if (ret < 0) {
> +			dev_warn(&devfreq->dev, "%s: setting resume frequency failed\n", __func__);
> +			continue;
> +		}
> +
> +		ret = devfreq_resume_device(devfreq);
> +		if (ret < 0)
> +			dev_warn(&devfreq->dev, "%s: governor resume failed\n", __func__);
> +	}
> +
> +	mutex_unlock(&devfreq_list_lock);
> +}
> +
> +/**
>   * devfreq_add_governor() - Add devfreq governor
>   * @governor:	the devfreq governor to be added
>   */
> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
> index 2de4e2e..555d024 100644
> --- a/include/linux/devfreq.h
> +++ b/include/linux/devfreq.h
> @@ -171,6 +171,9 @@ struct devfreq {
>  	struct notifier_block nb;
>  	struct delayed_work work;
>  
> +	unsigned long suspend_freq; /* freq during devfreq suspend */
> +	unsigned long resume_freq; /* freq restored after suspend cycle */
> +
>  	unsigned long previous_freq;
>  	struct devfreq_dev_status last_status;
>  
> @@ -211,6 +214,10 @@ extern void devm_devfreq_remove_device(struct device *dev,
>  extern int devfreq_suspend_device(struct devfreq *devfreq);
>  extern int devfreq_resume_device(struct devfreq *devfreq);
>  
> +/* Suspend/resume the entire Devfreq subsystem. */
> +void devfreq_suspend(void);
> +void devfreq_resume(void);
> +
>  /* Helper functions for devfreq user device driver with OPP. */
>  extern struct dev_pm_opp *devfreq_recommended_opp(struct device *dev,
>  					   unsigned long *freq, u32 flags);
> @@ -410,6 +417,9 @@ static inline int devfreq_update_stats(struct devfreq *df)
>  {
>  	return -EINVAL;
>  }
> +
> +static inline void devfreq_suspend(void) {}
> +static inline void devfreq_resume(void) {}
>  #endif /* CONFIG_PM_DEVFREQ */
>  
>  #endif /* __LINUX_DEVFREQ_H__ */
> 


-- 
Best Regards,
Chanwoo Choi