Re: [PATCH 06/12] PM / devfreq: Add cpu based scaling support to passive_governor

[andrew-sh.cheng <andrew-sh.cheng@mediatek.com>]

On Thu, 2020-05-28 at 15:14 +0900, Chanwoo Choi wrote:
> Hi Andrew-sh.Cheng,
> 
> Thanks for your posting. I like this approach absolutely.
> I think that it is necessary. When I developed the embedded product,
> I needed this feature always. 
> 
> I add the comments on below.
> 
> 
> And the following email is not valid. So, I dropped this email
> from Cc list.
> Saravana Kannan <skannan@codeaurora.org>
> 
> 
> On 5/20/20 12:43 PM, Andrew-sh.Cheng wrote:
> > From: Saravana Kannan <skannan@codeaurora.org>
> > 
> > Many CPU architectures have caches that can scale independent of the
> > CPUs. Frequency scaling of the caches is necessary to make sure that the
> > cache is not a performance bottleneck that leads to poor performance and
> > power. The same idea applies for RAM/DDR.
> > 
> > To achieve this, this patch adds support for cpu based scaling to the
> > passive governor. This is accomplished by taking the current frequency
> > of each CPU frequency domain and then adjust the frequency of the cache
> > (or any devfreq device) based on the frequency of the CPUs. It listens
> > to CPU frequency transition notifiers to keep itself up to date on the
> > current CPU frequency.
> > 
> > To decide the frequency of the device, the governor does one of the
> > following:
> > * Derives the optimal devfreq device opp from required-opps property of
> >   the parent cpu opp_table.
> > 
> > * Scales the device frequency in proportion to the CPU frequency. So, if
> >   the CPUs are running at their max frequency, the device runs at its
> >   max frequency. If the CPUs are running at their min frequency, the
> >   device runs at its min frequency. It is interpolated for frequencies
> >   in between.
> > 
> > Andrew-sh.Cheng change
> > dev_pm_opp_xlate_opp to dev_pm_opp_xlate_required_opp devfreq->max_freq
> > to devfreq->user_min_freq_req.data.freq.qos->min_freq.target_value
> > for kernel-5.7
> > 
> > Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
> > [Sibi: Integrated cpu-freqmap governor into passive_governor]
> > Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
> > Signed-off-by: Andrew-sh.Cheng <andrew-sh.cheng@mediatek.com>
> > ---
> >  drivers/devfreq/Kconfig            |   2 +
> >  drivers/devfreq/governor_passive.c | 278 ++++++++++++++++++++++++++++++++++---
> >  include/linux/devfreq.h            |  40 +++++-
> >  3 files changed, 299 insertions(+), 21 deletions(-)
> > 
> > diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
> > index 0b1df12e0f21..d9067950af6a 100644
> > --- a/drivers/devfreq/Kconfig
> > +++ b/drivers/devfreq/Kconfig
> > @@ -73,6 +73,8 @@ config DEVFREQ_GOV_PASSIVE
> >  	  device. This governor does not change the frequency by itself
> >  	  through sysfs entries. The passive governor recommends that
> >  	  devfreq device uses the OPP table to get the frequency/voltage.
> > +	  Alternatively the governor can also be chosen to scale based on
> > +	  the online CPUs current frequency.
> >  
> >  comment "DEVFREQ Drivers"
> >  
> > diff --git a/drivers/devfreq/governor_passive.c b/drivers/devfreq/governor_passive.c
> > index 2d67d6c12dce..7dcda02a5bb7 100644
> > --- a/drivers/devfreq/governor_passive.c
> > +++ b/drivers/devfreq/governor_passive.c
> > @@ -8,11 +8,89 @@
> >   */
> >  
> >  #include <linux/module.h>
> > +#include <linux/cpu.h>
> > +#include <linux/cpufreq.h>
> > +#include <linux/cpumask.h>
> >  #include <linux/device.h>
> >  #include <linux/devfreq.h>
> > +#include <linux/slab.h>
> >  #include "governor.h"
> >  
> > -static int devfreq_passive_get_target_freq(struct devfreq *devfreq,
> > +static unsigned int xlate_cpufreq_to_devfreq(struct devfreq_passive_data *data,
> 
> Need to change 'unsigned int' to 'unsigned long'
Get it.
> .
> 
> > +					     unsigned int cpu)
> > +{
> > +	unsigned int cpu_min, cpu_max, dev_min, dev_max, cpu_percent, max_state;
> 
> Better to define them separately as following and then need to rename
> the variable. Usually, use the 'min_freq' and 'max_freq' word for
> the minimum/maximum frequency.
> 
> 	unsigned int cpu_min_freq, cpu_max_freq, cpu_curr_freq, cpu_percent;
> 	unsigned long dev_min_freq, dev_max_freq, dev_max_state,
> 
> The devfreq used 'unsigned long'. The cpufreq used 'unsigned long'
> and 'unsigned int'. You need to handle them properly.
Get it.
For cpu_freq, I separate it into "unsigned long cpu_curr_freq" and
"unsigned int cpu_curr_freq_khz"
> 
> 
> > +	struct devfreq_cpu_state *cpu_state = data->cpu_state[cpu];
> > +	struct devfreq *devfreq = (struct devfreq *)data->this;
> > +	unsigned long *freq_table = devfreq->profile->freq_table;
> 
> In this function, use 'cpu' work for cpufreq and use 'dev' for devfreq.
> So, I think 'dev_freq_table' is proper name instead of 'freq_table'
> for the readability.
> 
> 	freq_table -> dev_freq_table
> 
> > +	struct dev_pm_opp *opp = NULL, *cpu_opp = NULL;
> 
> In the get_target_freq_with_devfreq(), use 'p_opp' indicating
> the OPP of parent device. For the consistency, I think that
> use 'p_opp' instead of 'cpu_opp'. 
> 
> > +	unsigned long cpu_freq, freq;
> 
> Define the 'cpu_freq' on above with cpu_min_freq/cpu_max_freq definition.
> 	cpu_freq -> cpu_curr_freq.
Get it.
Will modify them for readability.
> 
> > +
> > +	if (!cpu_state || cpu_state->first_cpu != cpu ||
> > +	    !cpu_state->opp_table || !devfreq->opp_table)
> > +		return 0;
> > +
> > +	cpu_freq = cpu_state->freq * 1000;
> > +	cpu_opp = devfreq_recommended_opp(cpu_state->dev, &cpu_freq, 0);
> > +	if (IS_ERR(cpu_opp))
> > +		return 0;
> > +
> > +	opp = dev_pm_opp_xlate_required_opp(cpu_state->opp_table,
> > +					    devfreq->opp_table, cpu_opp);
> > +	dev_pm_opp_put(cpu_opp);
> > +
> > +	if (!IS_ERR(opp)) {
> > +		freq = dev_pm_opp_get_freq(opp);
> > +		dev_pm_opp_put(opp);
> 
> Better to add the 'out' goto statement.
> If you use 'goto out', you can reduce the one indentation
> without 'else' statement.
Get it.
> 	
> 
> > +	} else {
> 
> As I commented, when dev_pm_opp_xlate_required_opp() return successfully
> , use 'goto out'. We can remove 'else' and then reduce the unneeded indentation.
> 
> 
> > +		/* Use Interpolation if required opps is not available */
> > +		cpu_min = cpu_state->min_freq;
> > +		cpu_max = cpu_state->max_freq;
> > +		cpu_freq = cpu_state->freq;
> > +
> > +		if (freq_table) {
> > +			/* Get minimum frequency according to sorting order */
> > +			max_state = freq_table[devfreq->profile->max_state - 1];
> > +			if (freq_table[0] < max_state) {
> > +				dev_min = freq_table[0];
> > +				dev_max = max_state;
> > +			} else {
> > +				dev_min = max_state;
> > +				dev_max = freq_table[0];
> > +			}
> > +		} else {
> > +			if (devfreq->user_max_freq_req.data.freq.qos->max_freq.target_value
> > +			    <= devfreq->user_min_freq_req.data.freq.qos->min_freq.target_value)
> > +				return 0;
> > +			dev_min =
> > +			devfreq->user_min_freq_req.data.freq.qos->min_freq.target_value;
> > +			dev_max =
> > +			devfreq->user_max_freq_req.data.freq.qos->max_freq.target_value;
> 
> I think it is not proper to access the variable of pm_qos structure directly.
> Instead of direct access, you have to use the exported PM QoS function such as
> - pm_qos_read_value(devfreq->dev.parent, DEV_PM_QOS_MIN_FREQUENCY);
> - pm_qos_read_value(devfreq->dev.parent, DEV_PM_QOS_MAX_FREQUENCY);
Get it.
> 
> > +		}
> > +		cpu_percent = ((cpu_freq - cpu_min) * 100) / cpu_max - cpu_min;
> > +		freq = dev_min + mult_frac(dev_max - dev_min, cpu_percent, 100);
> > +	}
> 
> 
> I think that you better to add 'out' jump label as following:
> 
> out:
> 
> > +
> > +	return freq;
> > +}
> > +
> > +static int get_target_freq_with_cpufreq(struct devfreq *devfreq,
> > +					unsigned long *freq)
> > +{
> > +	struct devfreq_passive_data *p_data =
> > +				(struct devfreq_passive_data *)devfreq->data;
> > +	unsigned int cpu, target_freq = 0;
> 
> Need to define 'target_freq' with 'unsigned long' type.
Get it.
> 
> > +
> > +	for_each_online_cpu(cpu)
> > +		target_freq = max(target_freq,
> > +				  xlate_cpufreq_to_devfreq(p_data, cpu));
> > +
> > +	*freq = target_freq;
> > +
> > +	return 0;
> > +}
> > +
> > +static int get_target_freq_with_devfreq(struct devfreq *devfreq,
> >  					unsigned long *freq)
> >  {
> >  	struct devfreq_passive_data *p_data
> > @@ -23,16 +101,6 @@ static int devfreq_passive_get_target_freq(struct devfreq *devfreq,
> >  	int i, count, ret = 0;
> >  
> >  	/*
> > -	 * If the devfreq device with passive governor has the specific method
> > -	 * to determine the next frequency, should use the get_target_freq()
> > -	 * of struct devfreq_passive_data.
> > -	 */
> > -	if (p_data->get_target_freq) {
> > -		ret = p_data->get_target_freq(devfreq, freq);
> > -		goto out;
> > -	}
> > -
> > -	/*
> >  	 * If the parent and passive devfreq device uses the OPP table,
> >  	 * get the next frequency by using the OPP table.
> >  	 */
> > @@ -102,6 +170,37 @@ static int devfreq_passive_get_target_freq(struct devfreq *devfreq,
> >  	return ret;
> >  }
> >  
> > +static int devfreq_passive_get_target_freq(struct devfreq *devfreq,
> > +					   unsigned long *freq)
> > +{
> > +	struct devfreq_passive_data *p_data =
> > +				(struct devfreq_passive_data *)devfreq->data;
> > +	int ret;
> > +
> > +	/*
> > +	 * If the devfreq device with passive governor has the specific method
> > +	 * to determine the next frequency, should use the get_target_freq()
> > +	 * of struct devfreq_passive_data.
> > +	 */
> > +	if (p_data->get_target_freq)
> > +		return p_data->get_target_freq(devfreq, freq);
> > +
> > +	switch (p_data->parent_type) {
> > +	case DEVFREQ_PARENT_DEV:
> > +		ret = get_target_freq_with_devfreq(devfreq, freq);
> > +		break;
> > +	case CPUFREQ_PARENT_DEV:
> > +		ret = get_target_freq_with_cpufreq(devfreq, freq);
> > +		break;
> > +	default:
> > +		ret = -EINVAL;
> > +		dev_err(&devfreq->dev, "Invalid parent type\n");
> > +		break;
> > +	}
> > +
> > +	return ret;
> > +}
> > +
> >  static int update_devfreq_passive(struct devfreq *devfreq, unsigned long freq)
> >  {
> >  	int ret;
> > @@ -156,6 +255,140 @@ static int devfreq_passive_notifier_call(struct notifier_block *nb,
> >  	return NOTIFY_DONE;
> >  }
> >  
> > +static int cpufreq_passive_notifier_call(struct notifier_block *nb,
> > +					 unsigned long event, void *ptr)
> > +{
> > +	struct devfreq_passive_data *data =
> > +			container_of(nb, struct devfreq_passive_data, nb);
> > +	struct devfreq *devfreq = (struct devfreq *)data->this;
> > +	struct devfreq_cpu_state *cpu_state;
> > +	struct cpufreq_freqs *freq = ptr;
> 
> How about changing 'freq' to 'cpu_freqs'?
> 
> In the drivers/cpufreq/cpufreq.c, use 'freqs' name indicating
> the instance of 'struct cpufreq_freqs'. And in order to
> identfy, how about adding 'cpu_' prefix for variable name?
> 
> > +	unsigned int current_freq;
> 
> Need to define curr_freq with 'unsigned long' type
> and better to use 'curr_freq' variable name.
It is good to change current_freq to curr_freq, but why should it us
'unsigned long'?
I think it is 'unsigned int'.
> 
> > +	int ret;
> > +
> > +	if (event != CPUFREQ_POSTCHANGE || !freq ||
> > +	    !data->cpu_state[freq->policy->cpu])
> > +		return 0;
> > +
> > +	cpu_state = data->cpu_state[freq->policy->cpu];
> > +	if (cpu_state->freq == freq->new)
> > +		return 0;
> > +
> > +	/* Backup current freq and pre-update cpu state freq*/
> > +	current_freq = cpu_state->freq;
> > +	cpu_state->freq = freq->new;
> > +
> > +	mutex_lock(&devfreq->lock);
> > +	ret = update_devfreq(devfreq);
> > +	mutex_unlock(&devfreq->lock);
> > +	if (ret) {
> > +		cpu_state->freq = current_freq;
> > +		dev_err(&devfreq->dev, "Couldn't update the frequency.\n");
> > +		return ret;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int cpufreq_passive_register(struct devfreq_passive_data **p_data)
> > +{
> > +	struct devfreq_passive_data *data = *p_data;
> > +	struct devfreq *devfreq = (struct devfreq *)data->this;
> > +	struct device *dev = devfreq->dev.parent;
> > +	struct opp_table *opp_table = NULL;
> > +	struct devfreq_cpu_state *state;
> 
> For the readability, I thinkt 'cpu_state' is proper instead of 'state'.
Get it.
> 
> > +	struct cpufreq_policy *policy;
> > +	struct device *cpu_dev;
> > +	unsigned int cpu;
> > +	int ret;
> > +
> > +	get_online_cpus();
> 
> Add blank line.
Get it.
> 
> > +	data->nb.notifier_call = cpufreq_passive_notifier_call;
> > +	ret = cpufreq_register_notifier(&data->nb,
> > +					CPUFREQ_TRANSITION_NOTIFIER);
> > +	if (ret) {
> > +		dev_err(dev, "Couldn't register cpufreq notifier.\n");
> > +		data->nb.notifier_call = NULL;
> > +		goto out;
> > +	}
> > +
> > +	/* Populate devfreq_cpu_state */
> > +	for_each_online_cpu(cpu) {
> > +		if (data->cpu_state[cpu])
> > +			continue;
> > +
> > +		policy = cpufreq_cpu_get(cpu);
> 
> cpufreq_cpu_get() might return 'NULL'. I think you need to handle
> return value as following:
> 
> 		if (!policy) {
> 			ret = -EINVAL;
> 			goto out;
> 		} else if (PTR_ERR(policy) == -EPROBE_DEFER) {
> 			goto out;
> 		} else if (IS_ERR(policy) {
> 			ret = PTR_ERR(policy);
> 			dev_err(dev, "Couldn't get the cpufreq_poliy.\n");
> 			goto out;
> 		}
> 
> If cpufreq_cpu_get() return successfully, to do next.
> It reduces the one indentaion.
> 
> 
Get it.
> 
> > +		if (policy) {
> > +			state = kzalloc(sizeof(*state), GFP_KERNEL);
> > +			if (!state) {
> > +				ret = -ENOMEM;
> > +				goto out;
> > +			}
> > +
> > +			cpu_dev = get_cpu_device(cpu);
> > +			if (!cpu_dev) {
> > +				dev_err(dev, "Couldn't get cpu device.\n");
> > +				ret = -ENODEV;
> > +				goto out;
> > +			}
> > +
> > +			opp_table = dev_pm_opp_get_opp_table(cpu_dev);
> > +			if (IS_ERR(devfreq->opp_table)) {
> > +				ret = PTR_ERR(opp_table);
> > +				goto out;
> > +			}
> > +
> > +			state->dev = cpu_dev;
> > +			state->opp_table = opp_table;
> > +			state->first_cpu = cpumask_first(policy->related_cpus);
> > +			state->freq = policy->cur;
> > +			state->min_freq = policy->cpuinfo.min_freq;
> > +			state->max_freq = policy->cpuinfo.max_freq;
> > +			data->cpu_state[cpu] = state;
> 
> Add blank line.
> 
> > +			cpufreq_cpu_put(policy);
> > +		} else {
> > +			ret = -EPROBE_DEFER;
> > +			goto out;
> > +		}
> > +	}
> 
> Add blank line.
Get it.
> > +out:
> > +	put_online_cpus();
> > +	if (ret)
> > +		return ret;
> > +
> > +	/* Update devfreq */
> > +	mutex_lock(&devfreq->lock);
> > +	ret = update_devfreq(devfreq);
> > +	mutex_unlock(&devfreq->lock);
> > +	if (ret)
> > +		dev_err(dev, "Couldn't update the frequency.\n");
> > +
> > +	return ret;
> > +}
> > +
> > +static int cpufreq_passive_unregister(struct devfreq_passive_data **p_data)
> > +{
> > +	struct devfreq_passive_data *data = *p_data;
> > +	struct devfreq_cpu_state *cpu_state;
> > +	int cpu;
> > +
> > +	if (data->nb.notifier_call)
> > +		cpufreq_unregister_notifier(&data->nb,
> > +					    CPUFREQ_TRANSITION_NOTIFIER);
> > +
> > +	for_each_possible_cpu(cpu) {
> > +		cpu_state = data->cpu_state[cpu];
> > +		if (cpu_state) {
> > +			if (cpu_state->opp_table)
> > +				dev_pm_opp_put_opp_table(cpu_state->opp_table);
> > +			kfree(cpu_state);
> > +			cpu_state = NULL;
> > +		}
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >  static int devfreq_passive_event_handler(struct devfreq *devfreq,
> >  				unsigned int event, void *data)
> >  {
> > @@ -165,7 +398,7 @@ static int devfreq_passive_event_handler(struct devfreq *devfreq,
> >  	struct notifier_block *nb = &p_data->nb;
> >  	int ret = 0;
> >  
> > -	if (!parent)
> > +	if (p_data->parent_type == DEVFREQ_PARENT_DEV && !parent)
> >  		return -EPROBE_DEFER;
> 
> If you modify the devfreq_passive_event_handler() as following,
> you can move this condition for DEVFREQ_PARENT_DEV into 
> (register|unregister)_parent_dev_notifier.
> 
> 	switch (event) {                                                                                  
> 	case DEVFREQ_GOV_START:                                               
> 		ret = register_parent_dev_notifier(p_data);
> 		break;
> 	case DEVFREQ_GOV_STOP:                                             
> 		ret = unregister_parent_dev_notifier(p_data);
> 		break;
> 	default: 
> 		ret = -EINVAL;
> 		break;
> 	}
>                                                                                               
> 	return ret;
> 
Get it.
> >  
> >  	switch (event) {
> > @@ -173,13 +406,24 @@ static int devfreq_passive_event_handler(struct devfreq *devfreq,
> >  		if (!p_data->this)
> >  			p_data->this = devfreq;
> >  
> > -		nb->notifier_call = devfreq_passive_notifier_call;
> > -		ret = devfreq_register_notifier(parent, nb,
> > -					DEVFREQ_TRANSITION_NOTIFIER);
> > +		if (p_data->parent_type == DEVFREQ_PARENT_DEV) {
> > +			nb->notifier_call = devfreq_passive_notifier_call;
> > +			ret = devfreq_register_notifier(parent, nb,
> > +						DEVFREQ_TRANSITION_NOTIFIER);
> > +		} else if (p_data->parent_type == CPUFREQ_PARENT_DEV) {
> > +			ret = cpufreq_passive_register(&p_data);
> 
> I think that we better to collect the code related to notifier registration
> into one function like devfreq_pass_register_notifier() instead of
> cpufreq_passive_register() as following: I think it is more simple and readable.
> 
> If you have more proper function name of register_parent_dev_notifier,
> please give your opinion.
> 
> 	int register_parent_dev_notifier(struct devfreq_passive_data **p_data)
> 		switch (p_data->parent_type) {
> 		case DEVFREQ_PARENT_DEV:
> 			nb->notifier_call = devfreq_passive_notifier_call;
> 			ret = devfreq_register_notifier(parent, nb,
> 			break;
> 		case CPUFREQ_PARENT_DEV:
> 			cpufreq_register_notifier(...)
> 			...
> 			break;
> 		}
Not fully understanding.
Do you mean expanding cpufreq_passive_register()?
I think leave it in function will be with clean for this code segment.

> 		
> 
> > +		} else {
> > +			ret = -EINVAL;
> > +		}
> >  		break;
> >  	case DEVFREQ_GOV_STOP:
> > -		WARN_ON(devfreq_unregister_notifier(parent, nb,
> > -					DEVFREQ_TRANSITION_NOTIFIER));
> > +		if (p_data->parent_type == DEVFREQ_PARENT_DEV)
> > +			WARN_ON(devfreq_unregister_notifier(parent, nb,
> > +						DEVFREQ_TRANSITION_NOTIFIER));
> > +		else if (p_data->parent_type == CPUFREQ_PARENT_DEV)
> > +			cpufreq_passive_unregister(&p_data);
> > +		else
> > +			ret = -EINVAL;
> 
> ditto. unregister_parent_dev_notifier(struct devfreq_passive_data **p_data)
Get it.
> 
> >  		break;
> >  	default:
> >  		break;
> > diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
> > index a4b19d593151..04ce576fd6f1 100644
> > --- a/include/linux/devfreq.h
> > +++ b/include/linux/devfreq.h
> > @@ -278,6 +278,32 @@ struct devfreq_simple_ondemand_data {
> >  
> >  #if IS_ENABLED(CONFIG_DEVFREQ_GOV_PASSIVE)
> >  /**
> > + * struct devfreq_cpu_state - holds the per-cpu state
> > + * @freq:	the current frequency of the cpu.
> > + * @min_freq:	the min frequency of the cpu.
> > + * @max_freq:	the max frequency of the cpu.
> > + * @first_cpu:	the cpumask of the first cpu of a policy.
> > + * @dev:	reference to cpu device.
> > + * @opp_table:	reference to cpu opp table.
> > + *
> > + * This structure stores the required cpu_state of a cpu.
> > + * This is auto-populated by the governor.
> > + */
> > +struct devfreq_cpu_state {> +	unsigned int freq;
> 
> It is better to change from 'freq' to 'curr_freq'
> for more correct expression.
Get it.
> 
> > +	unsigned int min_freq;
> > +	unsigned int max_freq;
> > +	unsigned int first_cpu;
> > +	struct device *dev;
> 
> How about changing the name 'dev' to 'cpu_dev'?
Okay.
> 
> 
> > +	struct opp_table *opp_table;
> > +};
> 
> devfreq_cpu_state is only handled by within driver/devfreq/governor_passive.c.
> 
> So, you can move it into drivers/devfreq/governor_passive.c
> and just add the definition into include/linux/devfreq.h as following:
> It is able to prevent the access of variable of 'struct devfreq_cpu_state'
> outside.
> 
> 	struct devfreq_cpu_state;
Get it.
> 
> > +
> > +enum devfreq_parent_dev_type {
> > +	DEVFREQ_PARENT_DEV,
> > +	CPUFREQ_PARENT_DEV,
> > +};
> > +
> > +/**
> >   * struct devfreq_passive_data - ``void *data`` fed to struct devfreq
> >   *	and devfreq_add_device
> >   * @parent:	the devfreq instance of parent device.
> > @@ -288,13 +314,15 @@ struct devfreq_simple_ondemand_data {
> >   *			using governors except for passive governor.
> >   *			If the devfreq device has the specific method to decide
> >   *			the next frequency, should use this callback.
> > - * @this:	the devfreq instance of own device.
> > - * @nb:		the notifier block for DEVFREQ_TRANSITION_NOTIFIER list
> > + * @parent_type		parent type of the device
> 
> Need to add ':' at the end of word. -> "parent_type:".
> 
> > + * @this:		the devfreq instance of own device.
> > + * @nb:			the notifier block for DEVFREQ_TRANSITION_NOTIFIER list
> 
> I knew that you make them with same indentation.
> But, actually, it is not related to this patch like clean-up code.
> Even if it is not pretty, you better to don't touch 'this' and 'nb' indentaion.
Get it.
> 
> > + * @cpu_state:		the state min/max/current frequency of all online cpu's
> >   *
> >   * The devfreq_passive_data have to set the devfreq instance of parent
> >   * device with governors except for the passive governor. But, don't need to
> > - * initialize the 'this' and 'nb' field because the devfreq core will handle
> > - * them.
> > + * initialize the 'this', 'nb' and 'cpu_state' field because the devfreq core
> > + * will handle them.
> >   */
> >  struct devfreq_passive_data {
> >  	/* Should set the devfreq instance of parent device */
> > @@ -303,9 +331,13 @@ struct devfreq_passive_data {
> >  	/* Optional callback to decide the next frequency of passvice device */
> >  	int (*get_target_freq)(struct devfreq *this, unsigned long *freq);
> >  
> > +	/* Should set the type of parent device */
> > +	enum devfreq_parent_dev_type parent_type;
> > +
> >  	/* For passive governor's internal use. Don't need to set them */
> >  	struct devfreq *this;
> >  	struct notifier_block nb;
> > +	struct devfreq_cpu_state *cpu_state[NR_CPUS];
> >  };
> >  #endif
> >  
> > 
> 
> 

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