Re: [PATCH v8 4/6] PM / devfreq: Introduce get_freq_range helper

[Leonard Crestez <leonard.crestez@nxp.com>]

On 25.09.2019 04:32, Chanwoo Choi wrote:
> On 19. 9. 24. 오후 7:11, Leonard Crestez wrote:
>> Moving handling of min/max freq to a single function and call it from
>> update_devfreq and for printing min/max freq values in sysfs.
>>
>> This changes the behavior of out-of-range min_freq/max_freq: clamping
>> is now done at evaluation time. This means that if an out-of-range
>> constraint is imposed by sysfs and it later becomes valid then it will
>> be enforced.
>>
>> Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
>> Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
>> ---
>>   drivers/devfreq/devfreq.c | 112 ++++++++++++++++++++++----------------
>>   1 file changed, 64 insertions(+), 48 deletions(-)
>>
>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>> index 4a878baa809e..eee403e70c84 100644
>> --- a/drivers/devfreq/devfreq.c
>> +++ b/drivers/devfreq/devfreq.c
>> @@ -96,10 +96,54 @@ static unsigned long find_available_max_freq(struct devfreq *devfreq)
>>   		dev_pm_opp_put(opp);
>>   
>>   	return max_freq;
>>   }
>>   
>> +/**
>> + * get_freq_range() - Get the current freq range
>> + * @devfreq:	the devfreq instance
>> + * @min_freq:	the min frequency
>> + * @max_freq:	the max frequency
>> + *
>> + * This takes into consideration all constraints.
>> + */
>> +static void get_freq_range(struct devfreq *devfreq,
>> +			   unsigned long *min_freq,
>> +			   unsigned long *max_freq)
>> +{
>> +	unsigned long *freq_table = devfreq->profile->freq_table;
>> +
>> +	lockdep_assert_held(&devfreq->lock);
>> +
>> +	/*
>> +	 * Init min/max frequency from freq table.
> 
> Init -> Initialize
> min/max -> minimum/maximum
> 
>> +	 * Drivers can initialize this in either ascending or descending order
> 
> Drivers -> devfreq drivers
> 
>> +	 * and devfreq core supports both.
>> +	 */
> 
> 
> In result, I prefer to change the comments as following:
> 	/*
> 	 * Initialize the minimum/maximum frequency from freq_table.
>   	 * The devfreq drivers can initialize freq_table in either
> 	 * ascending or descending order and devfreq core supports both.
> 	 */

OK

>> +	if (freq_table[0] < freq_table[devfreq->profile->max_state - 1]) {
>> +		*min_freq = freq_table[0];
>> +		*max_freq = freq_table[devfreq->profile->max_state - 1];
>> +	} else {
>> +		*min_freq = freq_table[devfreq->profile->max_state - 1];
>> +		*max_freq = freq_table[0];
>> +	}
>> +
>> +	/* constraints from sysfs */
> 
> 'constraints' -> Constraint because first verb have to be used
> as the sigular verbs. Also, I think that have to enhance the comments
> I prefer to use following comments:
> 
> 	 /* Constraint minimum/maximum frequency from user input via sysfs */
> 
> 
> 
>> +	*min_freq = max(*min_freq, devfreq->min_freq);
>> +	*max_freq = min(*max_freq, devfreq->max_freq);
>> +
>> +	/* constraints from OPP interface */
> 
> ditto. I prefer to use following comments:
> 
> 	/* Constraint minimum/maximum frequency from OPP interface */
> 
> 
>> +	*min_freq = max(*min_freq, devfreq->scaling_min_freq);
>> +	/* scaling_max_freq can be zero on error */
> 
> Please remove it.
> 
>> +	if (devfreq->scaling_max_freq)
> 
> As I knew, devfreq->scaling_max_freq is never zero.
> So, it is always true. This if statement is needed.

It can happen if find_available_max_freq encounters an error when called 
from devfreq_notifier_call.

Maybe that should be separately fixed to set scaling_max_freq to a 
neutral value such as "ULONG_MAX" instead?

BTW: the devfreq_notifier_call function returns -EINVAL on error but it 
should return one of the NOTIFY_OK/DONE/STOP values instead. The OPP 
framework ignores notifier results but (-EINVAL & NOTIFY_STOP) evaluates 
as true so other notifiers will be skipped unintentionally.

>> +		*max_freq = min(*max_freq, devfreq->scaling_max_freq);
>> +
>> +	/* max_freq takes precedence over min_freq */
> 
> As I said, almost people know that min_freq have be under than max_freq.
> Please remove it. And until finishing the discussion on mailing list,
> please don't send the next version. If you just replied from my comment
> and then wait my next comment, we can save the time without replying
> the repetitive and same comment for same point.

This series makes it possible to set a min_freq higher than max_freq 
(for example via PM QoS from various devices).

It is not obvious that min_freq takes precedence over max_freq but the 
code is self-evident so I will remove the comment.

>> +	if (*min_freq > *max_freq)
>> +		*min_freq = *max_freq;
>> +}
>> +
>>   /**
>>    * devfreq_get_freq_level() - Lookup freq_table for the frequency
>>    * @devfreq:	the devfreq instance
>>    * @freq:	the target frequency
>>    */
>> @@ -349,20 +393,11 @@ int update_devfreq(struct devfreq *devfreq)
>>   
>>   	/* Reevaluate the proper frequency */
>>   	err = devfreq->governor->get_target_freq(devfreq, &freq);
>>   	if (err)
>>   		return err;
>> -
>> -	/*
>> -	 * Adjust the frequency with user freq, QoS and available freq.
>> -	 *
>> -	 * List from the highest priority
>> -	 * max_freq
>> -	 * min_freq
>> -	 */
>> -	max_freq = min(devfreq->scaling_max_freq, devfreq->max_freq);
>> -	min_freq = max(devfreq->scaling_min_freq, devfreq->min_freq);
>> +	get_freq_range(devfreq, &min_freq, &max_freq);
>>   
>>   	if (freq < min_freq) {
>>   		freq = min_freq;
>>   		flags &= ~DEVFREQ_FLAG_LEAST_UPPER_BOUND; /* Use GLB */
>>   	}
>> @@ -1298,40 +1333,28 @@ static ssize_t min_freq_store(struct device *dev, struct device_attribute *attr,
>>   	ret = sscanf(buf, "%lu", &value);
>>   	if (ret != 1)
>>   		return -EINVAL;
>>   
>>   	mutex_lock(&df->lock);
>> -
>> -	if (value) {
>> -		if (value > df->max_freq) {
>> -			ret = -EINVAL;
>> -			goto unlock;
>> -		}
>> -	} else {
>> -		unsigned long *freq_table = df->profile->freq_table;
>> -
>> -		/* Get minimum frequency according to sorting order */
>> -		if (freq_table[0] < freq_table[df->profile->max_state - 1])
>> -			value = freq_table[0];
>> -		else
>> -			value = freq_table[df->profile->max_state - 1];
>> -	}
>> -
>>   	df->min_freq = value;
>>   	update_devfreq(df);
>> -	ret = count;
>> -unlock:
>>   	mutex_unlock(&df->lock);
>> -	return ret;
>> +
>> +	return count;
>>   }
>>   
>>   static ssize_t min_freq_show(struct device *dev, struct device_attribute *attr,
>>   			     char *buf)
>>   {
>>   	struct devfreq *df = to_devfreq(dev);
>> +	unsigned long min_freq, max_freq;
>> +
>> +	mutex_lock(&df->lock);
>> +	get_freq_range(df, &min_freq, &max_freq);
>> +	mutex_unlock(&df->lock);
>>   
>> -	return sprintf(buf, "%lu\n", max(df->scaling_min_freq, df->min_freq));
>> +	return sprintf(buf, "%lu\n", min_freq);
>>   }
>>   
>>   static ssize_t max_freq_store(struct device *dev, struct device_attribute *attr,
>>   			      const char *buf, size_t count)
>>   {
>> @@ -1343,40 +1366,33 @@ static ssize_t max_freq_store(struct device *dev, struct device_attribute *attr,
>>   	if (ret != 1)
>>   		return -EINVAL;
>>   
>>   	mutex_lock(&df->lock);
>>   
>> -	if (value) {
>> -		if (value < df->min_freq) {
>> -			ret = -EINVAL;
>> -			goto unlock;
>> -		}
>> -	} else {
>> -		unsigned long *freq_table = df->profile->freq_table;
>> -
>> -		/* Get maximum frequency according to sorting order */
>> -		if (freq_table[0] < freq_table[df->profile->max_state - 1])
>> -			value = freq_table[df->profile->max_state - 1];
>> -		else
>> -			value = freq_table[0];
>> -	}
>> +	/* Interpret zero as "don't care" */
> 
> Please remove it. Also, the detailed comment for user have to add
> the documentation file.

OK

> 
>> +	if (!value)
>> +		value = ULONG_MAX;
>>   
>>   	df->max_freq = value;
>>   	update_devfreq(df);
>> -	ret = count;
>> -unlock:
>>   	mutex_unlock(&df->lock);
>> -	return ret;
>> +
>> +	return count;
>>   }
>>   static DEVICE_ATTR_RW(min_freq);
>>   
>>   static ssize_t max_freq_show(struct device *dev, struct device_attribute *attr,
>>   			     char *buf)
>>   {
>>   	struct devfreq *df = to_devfreq(dev);
>> +	unsigned long min_freq, max_freq;
>> +
>> +	mutex_lock(&df->lock);
>> +	get_freq_range(df, &min_freq, &max_freq);
>> +	mutex_unlock(&df->lock);
>>   
>> -	return sprintf(buf, "%lu\n", min(df->scaling_max_freq, df->max_freq));
>> +	return sprintf(buf, "%lu\n", max_freq);
>>   }
>>   static DEVICE_ATTR_RW(max_freq);
>>   
>>   static ssize_t available_frequencies_show(struct device *d,
>>   					  struct device_attribute *attr,
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