Message-ID: <2ae8604d-0da6-4243-1b92-81b3917d7d48@samsung.com>
Date:   Wed, 31 Mar 2021 17:27:10 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     "andrew-sh.cheng" <andrew-sh.cheng@...iatek.com>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Nishanth Menon <nm@...com>, Stephen Boyd <sboyd@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        srv_heupstream@...iatek.com, Sibi Sankar <sibis@...eaurora.org>
Subject: Re: [PATCH V8 1/8] PM / devfreq: Add cpu based scaling support to
 passive_governor

Hi,

On 3/31/21 5:03 PM, andrew-sh.cheng wrote:
> On Thu, 2021-03-25 at 17:14 +0900, Chanwoo Choi wrote:
>> Hi,
>>
>> You are missing to add these patches to linux-pm mailing list.
>> Need to send them to linu-pm ML.
>>
>> Also, before received this series, I tried to clean-up these patches
>> on testing branch[1]. So that I add my comment with my clean-up case.
>> [1] https://urldefense.com/v3/__https://git.kernel.org/pub/scm/linux/kernel/git/chanwoo/linux.git/log/?h=devfreq-testing-passive-gov__;!!CTRNKA9wMg0ARbw!zIrzeDp9vPnm1_SDzVPuzqdHn3zWie9DnfBXaA-j9-CSrVc6aR9_rJQQiw81_CgAPh9XRRs$ 
>>
>> And 'Saravana Kannan <skannan@...eaurora.org>' is wrong email address.
>> Please update the email or drop this email.
> 
> Hi Chanwoo,
> 
> Thank you for the advices.
> I will resend patch v9 (add to linux-pm ML), remove this patch, and note
> that my patch set base on
> https://git.kernel.org/pub/scm/linux/kernel/git/chanwoo/linux.git/log/?h=devfreq-testing-passive-gov

I has not yet test this patch[1] on devfreq-testing-passive-gov branch.
So that if possible, I'd like you to test your patches with this patch[1] 
and then if there is no problem, could you send the next patches with patch[1]?

[1]https://git.kernel.org/pub/scm/linux/kernel/git/chanwoo/linux.git/commit/?h=devfreq-testing-passive-gov&id=39c80d11a8f42dd63ecea1e0df595a0ceb83b454

> 
> 
>>
>>
>> On 3/23/21 8:33 PM, Andrew-sh.Cheng wrote:
>>> From: Saravana Kannan <skannan@...eaurora.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
>>> after kernel-5.7
>>> Don't return -EINVAL in devfreq_passive_event_handler()
>>> since it doesn't handle DEVFREQ_GOV_SUSPEND DEVFREQ_GOV_RESUME cases.
>>>
>>> Signed-off-by: Saravana Kannan <skannan@...eaurora.org>
>>> [Sibi: Integrated cpu-freqmap governor into passive_governor]
>>> Signed-off-by: Sibi Sankar <sibis@...eaurora.org>
>>> Signed-off-by: Andrew-sh.Cheng <andrew-sh.cheng@...iatek.com>
>>> ---
>>>  drivers/devfreq/Kconfig            |   2 +
>>>  drivers/devfreq/governor_passive.c | 329 +++++++++++++++++++++++++++++++++++--
>>>  include/linux/devfreq.h            |  29 +++-
>>>  3 files changed, 342 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
>>> index 00704efe6398..f56132b0ae64 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 b094132bd20b..9cc57b083839 100644
>>> --- a/drivers/devfreq/governor_passive.c
>>> +++ b/drivers/devfreq/governor_passive.c
>>> @@ -8,11 +8,103 @@
>>>   */
>>>  
>>>  #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,
>>> +struct devfreq_cpu_state {
>>> +	unsigned int curr_freq;
>>> +	unsigned int min_freq;
>>> +	unsigned int max_freq;
>>> +	unsigned int first_cpu;
>>> +	struct device *cpu_dev;
>>> +	struct opp_table *opp_table;
>>> +};
>>
>> As I knew, the previous version has the description of structure
>> as following:  I wan to add the description like below.
>>
>> And if you have no any objection, I'd like you to order
>> the variables as following and use 'dev' instead of 'cpu_dev'
>> because this patch use the 'cpu_state->cpu_dev' at the multiple points.
>> I think that 'cpu_state->dev' is better than 'cpu_state->cpu_dev'.
>> Also, I prefer to use 'cur_freq' instead of 'curr_freq'
>> because devfreq subsystem uses 'cur_freq' for expressing the 'current frequency'.
>>
>> /**                                                                             
>>  * struct devfreq_cpu_state - Hold the per-cpu data                              
>>  * @dev:        reference to cpu device.                                        
>>  * @first_cpu:  the cpumask of the first cpu of a policy.                       
>>  * @opp_table:  reference to cpu opp table.                                     
>>  * @cur_freq:   the current frequency of the cpu.                               
>>  * @min_freq:   the min frequency of the cpu.                                   
>>  * @max_freq:   the max frequency of the cpu.                                   
>>  *                                                                              
>>  * This structure stores the required cpu_data of a cpu.                        
>>  * This is auto-populated by the governor.                                      
>>  */                                                                             
>> struct devfreq_cpu_state {                                                       
>>          struct device *dev;                                                     
>>          unsigned int first_cpu;                                                 
>>
>>          struct opp_table *opp_table;                                            
>>          unsigned int cur_freq;                                                  
>>          unsigned int min_freq;                                                  
>>          unsigned int max_freq;                                                  
>> };               
>>
>>
>>> +
>>> +static unsigned long xlate_cpufreq_to_devfreq(struct devfreq_passive_data *data,
>>> +					      unsigned int cpu)
>>> +{
>>> +	unsigned int cpu_min_freq, cpu_max_freq, cpu_curr_freq_khz, cpu_percent;
>>> +	unsigned long dev_min_freq, dev_max_freq, dev_max_state;
>>> +
>>> +	struct devfreq_cpu_state *cpu_state = data->cpu_state[cpu];
>>> +	struct devfreq *devfreq = (struct devfreq *)data->this;
>>> +	unsigned long *dev_freq_table = devfreq->profile->freq_table;
>>> +	struct dev_pm_opp *opp = NULL, *p_opp = NULL;
>>> +	unsigned long cpu_curr_freq, freq;
>>> +
>>> +	if (!cpu_state || cpu_state->first_cpu != cpu ||
>>> +	    !cpu_state->opp_table || !devfreq->opp_table)
>>> +		return 0;
>>> +
>>> +	cpu_curr_freq = cpu_state->curr_freq * 1000;
>>> +	p_opp = devfreq_recommended_opp(cpu_state->cpu_dev, &cpu_curr_freq, 0);
>>> +	if (IS_ERR(p_opp))
>>> +		return 0;
>>> +
>>> +	opp = dev_pm_opp_xlate_required_opp(cpu_state->opp_table,
>>> +					    devfreq->opp_table, p_opp);
>>> +	dev_pm_opp_put(p_opp);
>>> +
>>> +	if (!IS_ERR(opp)) {
>>> +		freq = dev_pm_opp_get_freq(opp);
>>> +		dev_pm_opp_put(opp);
>>> +		goto out;
>>> +	}
>>> +
>>> +	/* Use Interpolation if required opps is not available */
>>> +	cpu_min_freq = cpu_state->min_freq;
>>> +	cpu_max_freq = cpu_state->max_freq;
>>> +	cpu_curr_freq_khz = cpu_state->curr_freq;
>>> +
>>> +	if (dev_freq_table) {
>>> +		/* Get minimum frequency according to sorting order */
>>> +		dev_max_state = dev_freq_table[devfreq->profile->max_state - 1];
>>> +		if (dev_freq_table[0] < dev_max_state) {
>>> +			dev_min_freq = dev_freq_table[0];
>>> +			dev_max_freq = dev_max_state;
>>> +		} else {
>>> +			dev_min_freq = dev_max_state;
>>> +			dev_max_freq = dev_freq_table[0];
>>> +		}
>>> +	} else {
>>> +		dev_min_freq = dev_pm_qos_read_value(devfreq->dev.parent,
>>> +						     DEV_PM_QOS_MIN_FREQUENCY);
>>> +		dev_max_freq = dev_pm_qos_read_value(devfreq->dev.parent,
>>> +						     DEV_PM_QOS_MAX_FREQUENCY);
>>> +
>>> +		if (dev_max_freq <= dev_min_freq)
>>> +			return 0;
>>> +	}
>>> +	cpu_percent = ((cpu_curr_freq_khz - cpu_min_freq) * 100) / cpu_max_freq - cpu_min_freq;
>>> +	freq = dev_min_freq + mult_frac(dev_max_freq - dev_min_freq, cpu_percent, 100);
>>> +
>>> +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;
>>> +	unsigned long target_freq = 0;
>>> +
>>> +	for_each_online_cpu(cpu)
>>> +		target_freq = max(target_freq,
>>> +				  xlate_cpufreq_to_devfreq(p_data, cpu));
>>> +
>>> +	*freq = target_freq;
>>> +
>>> +	return 0;
>>> +}
>>
>> As you knew, governor_passive.c was already used 
>> both 'dev_pm_opp_xlate_required_opp' and 'devfreq_recommended_opp'
>> to get the target from OPP. So, I wan to make the common function
>> like 'get_taget_freq_by_required_opp' as following:
>> If define 'get_taget_freq_by_required_opp' as following,
>> it will be used for get_target_freq_with_devfreq().
>> After finisied the review of this patch, I'll send the patch[2].
>> [2] https://urldefense.com/v3/__https://git.kernel.org/pub/scm/linux/kernel/git/chanwoo/linux.git/commit/?h=devfreq-testing-passive-gov&id=101c5a087586ab2b5cf3370166a7e39227ca83cf__;!!CTRNKA9wMg0ARbw!zIrzeDp9vPnm1_SDzVPuzqdHn3zWie9DnfBXaA-j9-CSrVc6aR9_rJQQiw81_CgA6mp3Yqo$ 
>>
>> For example but this code is not tested,
>> static unsigned long get_taget_freq_by_required_opp(struct device *p_dev,
>> 						struct opp_table *p_opp_table,
>> 						struct opp_table *opp_table,
>> 						unsigned long freq)
>> {
>> 	struct dev_pm_opp *opp = NULL, *p_opp = NULL;
>>
>> 	if (!p_dev || !p_opp_table || !opp_table || !freq)
>> 		return 0;
>>
>> 	p_opp = devfreq_recommended_opp(p_dev, &freq, 0);
>> 	if (IS_ERR(p_opp))
>> 		return 0;
>>
>> 	opp = dev_pm_opp_xlate_required_opp(p_opp_table, opp_table, p_opp);
>> 	dev_pm_opp_put(p_opp);
>>
>> 	if (IS_ERR(opp))
>> 		return 0;
>>
>> 	freq = dev_pm_opp_get_freq(opp);
>> 	dev_pm_opp_put(opp);
>>
>> 	return freq;
>> }
>>
>> static int get_target_freq_with_cpufreq(struct devfreq *devfreq,
>> 					unsigned long *target_freq)
>> {
>> 	struct devfreq_passive_data *p_data =
>> 				(struct devfreq_passive_data *)devfreq->data;
>> 	struct devfreq_cpu_data *cpu_data;
>> 	unsigned long cpu, cpu_cur, cpu_min, cpu_max, cpu_percent;
>> 	unsigned long dev_min, dev_max;
>> 	unsigned long freq = 0;
>>
>> 	for_each_online_cpu(cpu) {
>> 		cpu_data = p_data->cpu_data[cpu];
>> 		if (!cpu_data || cpu_data->first_cpu != cpu)
>> 			continue;
>>
>> 		/* Get target freq via required opps */
>> 		cpu_cur = cpu_data->cur_freq * HZ_PER_KHZ;
>> 		freq = get_taget_freq_by_required_opp(cpu_data->dev,
>> 					cpu_data->opp_table,
>> 					devfreq->opp_table, cpu_cur);
>> 		if (freq) {
>> 			*target_freq = max(freq, *target_freq);
>> 			continue;
>> 		}
>>
>> 		/* Use Interpolation if required opps is not available */
>> 		devfreq_get_freq_range(devfreq, &dev_min, &dev_max);
>>
>> 		cpu_min = cpu_data->min_freq;
>> 		cpu_max = cpu_data->max_freq;
>> 		cpu_cur = cpu_data->cur_freq;
>>
>> 		cpu_percent = ((cpu_cur - cpu_min) * 100) / cpu_max - cpu_min;
>> 		freq = dev_min + mult_frac(dev_max - dev_min, cpu_percent, 100);
>>
>> 		*target_freq = max(freq, *target_freq);
>> 	}
>>
>> 	return 0;
>> }
>>
>>> +
>>> +static int get_target_freq_with_devfreq(struct devfreq *devfreq,
>>>  					unsigned long *freq)
>>>  {
>>>  	struct devfreq_passive_data *p_data
>>> @@ -23,14 +115,6 @@ static int devfreq_passive_get_target_freq(struct devfreq *devfreq,
>>>  	int i, count;
>>>  
>>>  	/*
>>> -	 * 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);
>>> -
>>> -	/*
>>>  	 * If the parent and passive devfreq device uses the OPP table,
>>>  	 * get the next frequency by using the OPP table.
>>>  	 */
>>> @@ -98,6 +182,37 @@ static int devfreq_passive_get_target_freq(struct devfreq *devfreq,
>>>  	return 0;
>>>  }
>>>  
>>> +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 devfreq_passive_notifier_call(struct notifier_block *nb,
>>>  				unsigned long event, void *ptr)
>>>  {
>>> @@ -130,16 +245,200 @@ 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 *cpu_freq = ptr;
>>
>> Use 'freqs' variable name.  I prefer to use the same variable name
>> for both devfreq_freqs and cpufreq_freqs instance.
>>
>>> +	unsigned int curr_freq;
>>
>> As I commented above, better to use 'cur_frq' instead of 'curr_freq'
>> if there is no any special reason.
>>
>>> +	int ret;
>>> +
>>> +	if (event != CPUFREQ_POSTCHANGE || !cpu_freq ||
>>> +	    !data->cpu_state[cpu_freq->policy->cpu])
>>> +		return 0;
>>> +
>>> +	cpu_state = data->cpu_state[cpu_freq->policy->cpu];
>>> +	if (cpu_state->curr_freq == cpu_freq->new)
>>> +		return 0;
>>> +
>>> +	/* Backup current freq and pre-update cpu state freq*/
>>
>> I think that this commnet is not critial. So, please drop this comment.
>>
>>> +	curr_freq = cpu_state->curr_freq;
>>> +	cpu_state->curr_freq = cpu_freq->new;
>>> +
>>> +	mutex_lock(&devfreq->lock);
>>> +	ret = update_devfreq(devfreq);
>>
>> I recommend to use 'devfreq_update_target' instead of 'update_devfreq'
>> as following:
>> 	devfreq_update_target(devfreq, freqs->new);
>>
>>> +	mutex_unlock(&devfreq->lock);
>>> +	if (ret) {
>>> +		cpu_state->curr_freq = curr_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)
>>
>> In order to keep the consistent style of function name,
>> please change the name as following because devfreq defines
>> the function name as 'devfreq_regiter_notifier'
>> - cpufreq_passive_register -> cpufreq_passive_register_notifier
>>
>>> +{
>>> +	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 *cpu_state;
>>> +	struct cpufreq_policy *policy;
>>> +	struct device *cpu_dev;
>>> +	unsigned int cpu;
>>> +	int ret;
>>> +
>>> +	get_online_cpus();
>>> +
>>> +	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 */
>>
>> Don't need this comment. Please drop it.
>>
>>> +	for_each_online_cpu(cpu) {
>>> +		if (data->cpu_state[cpu])
>>> +			continue;
>>> +
>>> +		policy = cpufreq_cpu_get(cpu);
>>> +		if (!policy) {
>>> +			ret = -EINVAL;
>>> +			goto out;
>>> +		} else if (PTR_ERR(policy) == -EPROBE_DEFER) {
>>> +			ret = -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;
>>> +		}
>>
>> Use dev_err_probe() funciotn to handle hte EPROBE_DEFER.
>> It make code more simple.
>>
>>> +
>>> +		cpu_state = kzalloc(sizeof(*cpu_state), GFP_KERNEL);
>>> +		if (!cpu_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;
>>> +		}
>>> +
>>> +		cpu_state->cpu_dev = cpu_dev;
>>> +		cpu_state->opp_table = opp_table;
>>> +		cpu_state->first_cpu = cpumask_first(policy->related_cpus);
>>> +		cpu_state->curr_freq = policy->cur;
>>> +		cpu_state->min_freq = policy->cpuinfo.min_freq;
>>> +		cpu_state->max_freq = policy->cpuinfo.max_freq;
>>> +		data->cpu_state[cpu] = cpu_state;
>>> +
>>> +		cpufreq_cpu_put(policy);
>>> +	}
>>> +
>>> +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)
>>
>> As I commented above, please change the name as following:
>> - cpufreq_passive_unregister -> cpufreq_passive_unregister_notifier
>>
>>> +{
>>> +	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;
>>> +}
>>> +
>>> +int register_parent_dev_notifier(struct devfreq_passive_data **p_data)
>>> +{
>>> +	struct notifier_block *nb = &(*p_data)->nb;
>>> +	int ret = 0;
>>> +
>>> +	switch ((*p_data)->parent_type) {
>>> +	case DEVFREQ_PARENT_DEV:
>>> +		nb->notifier_call = devfreq_passive_notifier_call;
>>> +		ret = devfreq_register_notifier((struct devfreq *)(*p_data)->parent, nb,
>>> +						DEVFREQ_TRANSITION_NOTIFIER);
>>> +		break;
>>> +	case CPUFREQ_PARENT_DEV:
>>> +		ret = cpufreq_passive_register(p_data);
>>> +		break;
>>> +	default:
>>> +		ret = -EINVAL;
>>> +		break;
>>> +	}
>>> +	return ret;
>>> +}
>>> +
>>> +int unregister_parent_dev_notifier(struct devfreq_passive_data **p_data)
>>> +{
>>> +	int ret = 0;
>>> +
>>> +	switch ((*p_data)->parent_type) {
>>> +	case DEVFREQ_PARENT_DEV:
>>> +		WARN_ON(devfreq_unregister_notifier((struct devfreq *)(*p_data)->parent,
>>> +						    &(*p_data)->nb,
>>> +						    DEVFREQ_TRANSITION_NOTIFIER));
>>> +		break;
>>> +	case CPUFREQ_PARENT_DEV:
>>> +		cpufreq_passive_unregister(p_data);
>>> +		break;
>>> +	default:
>>> +		ret = -EINVAL;
>>> +		break;
>>> +	}
>>> +	return ret;
>>> +}
>>
>> I think that you don't need to define register_parent_dev_notifier
>> and unregister_parent_dev_notifier as the separate functions.
>>
>> Instead of the separate functions, just add the code
>> into devfreq_passive_event_handler.
>>
>>
>>> +
>>>  static int devfreq_passive_event_handler(struct devfreq *devfreq,
>>>  				unsigned int event, void *data)
>>>  {
>>>  	struct devfreq_passive_data *p_data
>>>  			= (struct devfreq_passive_data *)devfreq->data;
>>>  	struct devfreq *parent = (struct devfreq *)p_data->parent;
>>> -	struct notifier_block *nb = &p_data->nb;
>>>  	int ret = 0;
>>>  
>>> -	if (!parent)
>>> +	if (p_data->parent_type == DEVFREQ_PARENT_DEV && !parent)
>>>  		return -EPROBE_DEFER;
>>>  
>>>  	switch (event) {
>>> @@ -147,13 +446,11 @@ 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);
>>> +		ret = register_parent_dev_notifier(&p_data);
>>>  		break;
>>> +
>>>  	case DEVFREQ_GOV_STOP:
>>> -		WARN_ON(devfreq_unregister_notifier(parent, nb,
>>> -					DEVFREQ_TRANSITION_NOTIFIER));
>>> +		ret = unregister_parent_dev_notifier(&p_data);
>>>  		break;
>>>  	default:
>>>  		break;
>>> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
>>> index 26ea0850be9b..e0093b7c805c 100644
>>> --- a/include/linux/devfreq.h
>>> +++ b/include/linux/devfreq.h
>>> @@ -280,6 +280,25 @@ 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;
>>> +
>>> +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.
>>> @@ -290,13 +309,15 @@ 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.
>>> + * @parent_type:	parent type of the device
>>>   * @this:	the devfreq instance of own device.
>>>   * @nb:		the notifier block for DEVFREQ_TRANSITION_NOTIFIER list
>>> + * @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 */
>>> @@ -305,9 +326,13 @@ 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
>>>  
>>>
>>
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics

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