Re: [PATCH v4 05/20] PM / devfreq: Add new passive governor

[MyungJoo Ham]

>   
>  This patch adds the new passive governor for DEVFREQ framework. The following
> governors are already present and used for DVFS (Dynamic Voltage and Frequency
> Scaling) drivers. The following governors are independently used for one device
> driver which don't give the influence to other device drviers and also don't
> receive the effect from other device drivers.
> - ondemand / performance / powersave / userspace
> 
> The passive governor depends on operation of parent driver with specific
> governos extremely and is not able to decide the new frequency by oneself.
> According to the decided new frequency of parent driver with governor,
> the passive governor uses it to decide the appropriate frequency for own
> device driver. The passive governor must need the following information
> from device tree:
> - the source clock and OPP tables
> - the instance of parent device
> 
> For exameple,
> there are one more devfreq device drivers which need to change their source
> clock according to their utilization on runtime. But, they share the same
> power line (e.g., regulator). So, specific device driver is operated as parent
> with ondemand governor and then the rest device driver with passive governor
> is influenced by parent device.
> 
> Suggested-by: Myungjoo Ham <myungjoo.ham@xxxxxxxxxxx>
> Signed-off-by: Chanwoo Choi <cw00.choi@xxxxxxxxxxx>
> [linux.amoon: Tested on Odroid U3]
> Tested-by: Anand Moon <linux.amoon@xxxxxxxxx>
> ---
>  drivers/devfreq/Kconfig            |   9 ++++
>  drivers/devfreq/Makefile           |   1 +
>  drivers/devfreq/devfreq.c          |  47 ++++++++++++++++
>  drivers/devfreq/governor_passive.c | 108 +++++++++++++++++++++++++++++++++++++
>  include/linux/devfreq.h            |  15 ++++++
>  5 files changed, 180 insertions(+)
>  create mode 100644 drivers/devfreq/governor_passive.c
> 
> diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
> index 55ec774f794c..d03f635a93e1 100644
> --- a/drivers/devfreq/Kconfig
> +++ b/drivers/devfreq/Kconfig
> @@ -64,6 +64,15 @@ config DEVFREQ_GOV_USERSPACE
>  	  Otherwise, the governor does not change the frequnecy
>  	  given at the initialization.
>  
> +config DEVFREQ_GOV_PASSIVE
> +	tristate "Passive"
> +	help
> +	  Sets the frequency by other governors (simple_ondemand, performance,
> +	  powersave, usersapce) of a parent devfreq device. This governor
> +	  always has the dependency on the chosen frequency from paired
> +	  governor. This governor does not change the frequency by oneself
> +	  through sysfs entry.

	Sets the frequency based on the frequency of its parent devfreq
	device. This governor does not change the frequency by itself
	through sysfs entries.

> +
>  comment "DEVFREQ Drivers"
>  
>  config ARM_EXYNOS_BUS_DEVFREQ
> diff --git a/drivers/devfreq/Makefile b/drivers/devfreq/Makefile
> index 375ebbb4fcfb..f81c313b4b79 100644
> --- a/drivers/devfreq/Makefile
> +++ b/drivers/devfreq/Makefile
[]
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 984c5e9e7bdd..15e58779e4c0 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -190,6 +190,31 @@ static struct devfreq_governor *find_devfreq_governor(const char *name)
>  
>  /* Load monitoring helper functions for governors use */
>  
> +static int update_devfreq_passive(struct devfreq *devfreq, unsigned long freq)
> +{
> +	struct devfreq *passive;
> +	unsigned long rate;
> +	int ret;
> +
> +	list_for_each_entry(passive, &devfreq->passive_dev_list, passive_node) {
> +		if (!passive->governor)
> +			continue;
> +		rate = freq;
> +
> +		ret = passive->governor->get_target_freq(passive, &rate);
> +		if (ret)
> +			return ret;
> +
> +		ret = passive->profile->target(passive->dev.parent, &rate, 0);
> +		if (ret)
> +			return ret;
> +
> +		passive->previous_freq = rate;
> +	}
> +
> +	return 0;
> +}
> +
>  /**
>   * update_devfreq() - Reevaluate the device and configure frequency.
>   * @devfreq:	the devfreq instance.
> @@ -233,10 +258,18 @@ int update_devfreq(struct devfreq *devfreq)
>  		flags |= DEVFREQ_FLAG_LEAST_UPPER_BOUND; /* Use LUB */
>  	}
>  
> +	if (!list_empty(&devfreq->passive_dev_list)
> +		&& devfreq->previous_freq > freq)
> +		update_devfreq_passive(devfreq, freq);
> +

Could you please comment somewhere appropriate
that the dependent is going to be changed
before its parent if the frequency is going down.
(and after if going up)
And state why as well.

And, is this viable universally?

>  	err = devfreq->profile->target(devfreq->dev.parent, &freq, flags);
>  	if (err)
>  		return err;
>  
> +	if (!list_empty(&devfreq->passive_dev_list)
> +		&& devfreq->previous_freq < freq)
> +		update_devfreq_passive(devfreq, freq);
> +
>  	if (devfreq->profile->freq_table)
>  		if (devfreq_update_status(devfreq, freq))
>  			dev_err(&devfreq->dev,
> @@ -442,6 +475,10 @@ static void _remove_devfreq(struct devfreq *devfreq)
>  		return;
>  	}
>  	list_del(&devfreq->node);
> +	list_del(&devfreq->passive_node);
> +	if (!list_empty(&devfreq->passive_dev_list))
> +		list_del_init(&devfreq->passive_dev_list);
> +
>  	mutex_unlock(&devfreq_list_lock);
>  
>  	if (devfreq->governor)
> @@ -559,6 +596,16 @@ struct devfreq *devfreq_add_device(struct device *dev,
>  		goto err_init;
>  	}
>  
> +	if (!strncmp(devfreq->governor_name, "passive", 7)) {
> +		struct devfreq *parent_devfreq =
> +			((struct devfreq_passive_data *)data)->parent;
> +
> +		list_add(&devfreq->passive_node,
> +			&parent_devfreq->passive_dev_list);
> +	} else {
> +		INIT_LIST_HEAD(&devfreq->passive_dev_list);
> +	}
> +
>  	return devfreq;
>  
>  err_init:

This code has become too much invasive to devfreq.c
while being too special for the passive governor.

Why don't you add notifier chain to devfreq.c, which can be used
by anyone else as well, and use that notifier for passive governor?
You may refer to "cpufreq_register_notifier()" with 
CPUFREQ_TRANSITION_NOTIFIER.

> diff --git a/drivers/devfreq/governor_passive.c b/drivers/devfreq/governor_passive.c
> new file mode 100644

Then, utilizing notifier-block at governor_passive.c becomes possible.

You will also be able to write any frequency deciding code
inside governor_passive.c as well, not in devfreq.c.

> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
> index 6fa02a20eb63..95c54578a1b4 100644
> --- a/include/linux/devfreq.h
> +++ b/include/linux/devfreq.h
> @@ -177,6 +177,9 @@ struct devfreq {
>  	unsigned int *trans_table;
>  	unsigned long *time_in_state;
>  	unsigned long last_stat_updated;
> +
> +	struct list_head passive_dev_list;
> +	struct list_head passive_node;
>  };

You will need only one notifier head here.

>  
>  #if defined(CONFIG_PM_DEVFREQ)
> @@ -241,6 +244,18 @@ struct devfreq_simple_ondemand_data {
>  };
>  #endif
>  
> +/**
> + * struct devfreq_passive_data - void *data fed to struct devfreq
> + *	and devfreq_add_device
> + * @parent:		The parent devfreq device.
> + *
> + * If the fed devfreq_passive_data pointer is NULL to the governor,
> + * the governor return ERROR.
> + */
> +struct devfreq_passive_data {
> +	struct devfreq *parent;
> +};
> +

Please enclose the above with #if

>  #else /* !CONFIG_PM_DEVFREQ */
>  static inline struct devfreq *devfreq_add_device(struct device *dev,
>  					  struct devfreq_dev_profile *profile,
> -- 
> 1.9.1
>