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

From: Chanwoo Choi <[email-masked]>
Date: Thu, 26 Sep 2019 10:06:41 +0900

Hi,

On 19. 9. 26. 오전 5:55, Leonard Crestez wrote:
> 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 <[email-masked]>
>>> Reviewed-by: Matthias Kaehlcke <[email-masked]>
>>> ---
>>>   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.

If you are wondering this case, I think that have to fix
the possible issue on there instead of this point.

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

OK.

> 
> 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.

I agree. It is needed to fix the return value type.

> 
>>> +		*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,

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics

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