linux-kernel - Re: [PATCH] PM / devfreq: Init user limits from OPP limits, not viceversa

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Date:   Fri, 18 May 2018 08:20:30 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Brian Norris <briannorris@...omium.org>,
        Douglas Anderson <dianders@...omium.org>
Subject: Re: [PATCH] PM / devfreq: Init user limits from OPP limits, not
 viceversa

Hi,

On 2018년 05월 18일 01:35, Matthias Kaehlcke wrote:
> On Thu, May 17, 2018 at 10:07:56AM +0900, Chanwoo Choi wrote:
>> Hi,
>>
>> On 2018년 05월 17일 07:57, Matthias Kaehlcke wrote:
>>> Commit ab8f58ad72c4 ("PM / devfreq: Set min/max_freq when adding
>>> the devfreq device") introduced the initialization of the user
>>> limits min/max_freq from the lowest/highest available OPPs. Later
>>> commit f1d981eaecf8 ("PM / devfreq: Use the available min/max
>>> frequency") added scaling_min/max_freq, which actually represent
>>> the frequencies of the lowest/highest available OPP. scaling_min/
>>> max_freq are initialized with the values from min/max_freq, which
>>> is totally correct in the context, but a bit awkward to read.
>>>
>>> Swap the initialization and assign scaling_min/max_freq with the
>>> OPP freqs and then the user limts min/max_freq with scaling_min/
>>> max_freq.
>>>
>>> Needless to say that this change is a NOP, intended to improve
>>> readability.
>>>
>>> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
>>> ---
>>> Additional context: I'm considering to introduce the concept of
>>> a devfreq policy, which would probably move min/max_freq inside
>>> of a struct policy, this would make the initialization even
>>> more awkward to read. If this moves forward I might also propose
>>> to rename scaling_min/max_freq to something like min/max_opp_freq
>>> to avoid confusion with the frequencies in the policy (cpufreq uses
>>> scaling_min/max_freq for the sysfs attributes of the policy
>>> limits).
>>>
>>>  drivers/devfreq/devfreq.c | 12 ++++++------
>>>  1 file changed, 6 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>> index fe2af6aa88fc..0057ef5b0a98 100644
>>> --- a/drivers/devfreq/devfreq.c
>>> +++ b/drivers/devfreq/devfreq.c
>>> @@ -604,21 +604,21 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>>  		mutex_lock(&devfreq->lock);
>>>  	}
>>>  
>>> -	devfreq->min_freq = find_available_min_freq(devfreq);
>>> -	if (!devfreq->min_freq) {
>>> +	devfreq->scaling_min_freq = find_available_min_freq(devfreq);
>>> +	if (!devfreq->scaling_min_freq) {
>>>  		mutex_unlock(&devfreq->lock);
>>>  		err = -EINVAL;
>>>  		goto err_dev;
>>>  	}
>>> -	devfreq->scaling_min_freq = devfreq->min_freq;
>>> +	devfreq->min_freq = devfreq->scaling_min_freq;
>>>  
>>> -	devfreq->max_freq = find_available_max_freq(devfreq);
>>> -	if (!devfreq->max_freq) {
>>> +	devfreq->scaling_max_freq = find_available_max_freq(devfreq);
>>> +	if (!devfreq->scaling_max_freq) {
>>>  		mutex_unlock(&devfreq->lock);
>>>  		err = -EINVAL;
>>>  		goto err_dev;
>>>  	}
>>> -	devfreq->scaling_max_freq = devfreq->max_freq;
>>> +	devfreq->max_freq = devfreq->scaling_max_freq;
>>>  
>>>  	dev_set_name(&devfreq->dev, "devfreq%d",
>>>  				atomic_inc_return(&devfreq_no));
>>>
>>
>> This patch just clean-up codes related to min/max_freq and scaling_min/max_freq.
>> It seems be good.
>>
>> Reviewed-by: Chanwoo Choi <cw00.choi@...sung.com>
> 
> Thanks for the review!
> 
>> But, I don't want to change the name from 'scaling_min/max_freq'
>> to 'min/max_opp_freq'.
> 
> It's obviously up to you in the end, and I won't insist if you are
> convinced that scaling_min/max_freq is the better name (I suggest to
> make this judgement after a new revision of the policy patch [1],
> which likely will introduce another pair of frequencies, and naming
> can help to clearly differentiate between them).
> 
>> You can check the meaning of variables in comment of struct devfreq.
> 
> This is true, but ideally code should be as self-explaining as
> possible (without becoming too verbose ;-), and variable/function
> names are a key element for that.

I don't want to use the framework name for specific variable.

> 
> Best regards
> 
> Matthias
> 
> [1] https://patchwork.kernel.org/patch/10401999/
> 
> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics