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Subject: Re: [PATCH V8 1/8] PM / devfreq: Add cpu based scaling support to
 passive_governor
From:   Chanwoo Choi <cw00.choi@samsung.com>
To:     "andrew-sh.cheng" <andrew-sh.cheng@mediatek.com>
Cc:     MyungJoo Ham <myungjoo.ham@samsung.com>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Nishanth Menon <nm@ti.com>, Stephen Boyd <sboyd@kernel.org>,
        Liam Girdwood <lgirdwood@gmail.com>,
        Mark Brown <broonie@kernel.org>, linux-pm@vger.kernel.org,
        devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org,
        srv_heupstream@mediatek.com, Sibi Sankar <sibis@codeaurora.org>
Organization: Samsung Electronics
Message-ID: <cad52436-b291-05bf-236f-7b7cb1fdbbff@samsung.com>
Date:   Wed, 31 Mar 2021 17:35:34 +0900
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        <1616499241-4906-2-git-send-email-andrew-sh.cheng@mediatek.com>
        <233a3bd6-7ab1-5da2-9184-a745eb253d86@samsung.com>
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On 3/31/21 5:27 PM, Chanwoo Choi wrote:
> 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@codeaurora.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


Sorry for the confusion. I make the devfreq-testing-passive-gov[1]
branch based on latest devfreq-next branch.
[1] https://git.kernel.org/pub/scm/linux/kernel/git/chanwoo/linux.git/log/?h=devfreq-testing-passive-gov

First of all, if possible, I want to test them[1] with your patches in this series.
And then if there are no any problem, please let me know. After confirmed from you,
I'll send the patches of devfreq-testing-passive-gov[1] branch.
How about that?


> 
>>
>>
>>>
>>>
>>> On 3/23/21 8:33 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
>>>> 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@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 | 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