linux-kernel - Re: [PATCH v4 2/2] PM / devfreq: Add governor attribute flag for specifc sysfs nodes

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Date:   Thu, 22 Oct 2020 11:47:02 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Dmitry Osipenko <digetx@...il.com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org
Cc:     lukasz.luba@....com, enric.balletbo@...labora.com,
        hl@...k-chips.com, thierry.reding@...il.com, jonathanh@...dia.com,
        abel.vesa@....com, k.konieczny@...sung.com,
        b.zolnierkie@...sung.com, chanwoo@...nel.org,
        myungjoo.ham@...sung.com, kyungmin.park@...sung.com
Subject: Re: [PATCH v4 2/2] PM / devfreq: Add governor attribute flag for
 specifc sysfs nodes

On 10/22/20 11:30 AM, Dmitry Osipenko wrote:
> Hello Chanwoo,
> 
> 20.10.2020 06:04, Chanwoo Choi пишет:
>> @@ -1354,55 +1365,71 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
>>  	struct devfreq *df = to_devfreq(dev);
>>  	int ret;
>>  	char str_governor[DEVFREQ_NAME_LEN + 1];
>> -	const struct devfreq_governor *governor, *prev_governor;
>> +	const struct devfreq_governor *new_governor, *prev_governor;
>>  
>>  	if (!df->governor)
>>  		return -EINVAL;
>> +	prev_governor = df->governor;
>>  
>>  	ret = sscanf(buf, "%" __stringify(DEVFREQ_NAME_LEN) "s", str_governor);
>>  	if (ret != 1)
>>  		return -EINVAL;
>>  
>>  	mutex_lock(&devfreq_list_lock);
>> -	governor = try_then_request_governor(str_governor);
>> -	if (IS_ERR(governor)) {
>> -		ret = PTR_ERR(governor);
>> +	new_governor = try_then_request_governor(str_governor);
>> +	if (IS_ERR(new_governor)) {
>> +		ret = PTR_ERR(new_governor);
>>  		goto out;
>>  	}
>> -	if (df->governor == governor) {
>> +	if (prev_governor == new_governor) {
>>  		ret = 0;
>>  		goto out;
>> -	} else if (IS_SUPPORTED_FLAG(df->governor->flags, IMMUTABLE)
>> -		|| IS_SUPPORTED_FLAG(governor->flags, IMMUTABLE)) {
>> +	} else if (IS_SUPPORTED_FLAG(prev_governor->flags, IMMUTABLE)
>> +		|| IS_SUPPORTED_FLAG(new_governor->flags, IMMUTABLE)) {
>>  		ret = -EINVAL;
>>  		goto out;
>>  	}
>>  
>> -	ret = df->governor->event_handler(df, DEVFREQ_GOV_STOP, NULL);
>> +	/*
>> +	 * Stop the previous governor and remove the specific sysfs files
>> +	 * which depend on previous governor.
>> +	 */
>> +	ret = prev_governor->event_handler(df, DEVFREQ_GOV_STOP, NULL);
>>  	if (ret) {
>>  		dev_warn(dev, "%s: Governor %s not stopped(%d)\n",
>> -			 __func__, df->governor->name, ret);
>> +			 __func__, prev_governor->name, ret);
>>  		goto out;
>>  	}
>>  
>> -	prev_governor = df->governor;
>> -	df->governor = governor;
>> -	strncpy(df->governor_name, governor->name, DEVFREQ_NAME_LEN);
>> -	ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
>> +	remove_sysfs_files(df, prev_governor);
>> +
>> +	/*
>> +	 * Start the new governor and create the specific sysfs files
>> +	 * which depend on new governor.
>> +	 */
>> +	strncpy(df->governor_name, new_governor->name, DEVFREQ_NAME_LEN);
>> +	ret = new_governor->event_handler(df, DEVFREQ_GOV_START, NULL);
> 
> The "df->governor = new_governor" needs to be set before invocation of
> the event_handler(GOV_START) because governors like a
> performance-governor need to have the df->governor being set before the
> GOV_START callback, otherwise performance governor will use
> devfreq->prev_governor->get_target_freq() in devfreq_update_target(),
> thus setting a wrong (non-max) freq.

You're right. It is my mistake. Thanks for your detailed review.

> 
>>  	if (ret) {
>>  		dev_warn(dev, "%s: Governor %s not started(%d)\n",
>> -			 __func__, df->governor->name, ret);
>> -		df->governor = prev_governor;
>> +			 __func__, new_governor->name, ret);
>>  		strncpy(df->governor_name, prev_governor->name,
>>  			DEVFREQ_NAME_LEN);
>> -		ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
> 
> Same here.

OK.

> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics