linux-kernel - Re: [PATCH v3 3/8] PM / devfreq: Show the available min/max frequency through sysfs node

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Date:   Thu, 12 Oct 2017 13:08:05 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     cwchoi00@...il.com,
        "myungjoo.ham@...sung.com" <myungjoo.ham@...sung.com>
Cc:     Kyungmin Park <kyungmin.park@...sung.com>,
        "rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
        Inki Dae <inki.dae@...sung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v3 3/8] PM / devfreq: Show the available min/max
 frequency through sysfs node

On 2017년 10월 11일 21:57, Chanwoo Choi wrote:
> On Wed, Oct 11, 2017 at 8:15 PM, MyungJoo Ham <myungjoo.ham@...sung.com> wrote:
>>> The existing {min|max}_freq sysfs nodes don't consider whether min/max_freq
>>> are available or not. Those sysfs nodes show just the stored value
>>> in the struct devfreq.
>>>
>>> The devfreq uses the OPP interface and then dev_pm_opp_{disable|add}()
>>> might change the state of the device's supported frequency. This patch
>>> shows the available minimum and maximum frequency through sysfs node.
>>>
>>> Signed-off-by: Chanwoo Choi <cw00.choi@...sung.com>
>>> ---
>>>  drivers/devfreq/devfreq.c | 18 ++++++++++++++++--
>>>  1 file changed, 16 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>> index 2ce1fd0a1324..799a0cf75d39 100644
>>> --- a/drivers/devfreq/devfreq.c
>>> +++ b/drivers/devfreq/devfreq.c
>>> @@ -1128,7 +1128,14 @@ static ssize_t min_freq_store(struct device *dev, struct device_attribute *attr,
>>>  static ssize_t min_freq_show(struct device *dev, struct device_attribute *attr,
>>>                            char *buf)
>>>  {
>>> -     return sprintf(buf, "%lu\n", to_devfreq(dev)->min_freq);
>>> +     struct devfreq *df = to_devfreq(dev);
>>> +     unsigned long min_freq = to_devfreq(dev)->min_freq;
>>> +     unsigned long available_min_freq = find_available_min_freq(df);
>>> +
>>> +     if (available_min_freq != 0 && min_freq < available_min_freq)
>>
>> nitpick:
>>
>> If available_min_freq == 0,
>> it can't be min_freq < available_min_freq anyway;
>> it's unsigned.
> 
> If the dev_pm_opp_find_*() return the error in the find_available_min_freq(),
> avaiable_min_freq is zero. So, if available_min_freq is zero,
> min_freq_show doesn't need to compare 'min_freq < available_min_freq'.
> 
> In result, if 'available_min_freq' is zero, min_freq_show() only considers
> the 'min_freq' variable.

I'll modify this patch as following: How about that?

+       if (available_min_freq == 0)
+               goto out;
+       else if (min_freq < available_min_freq)
+               min_freq = available_min_freq;
+
+out:
+       return sprintf(buf, "%lu\n", min_freq);


>>
>>> +             min_freq = available_min_freq;
>>> +
>>> +     return sprintf(buf, "%lu\n", min_freq);
>>>  }
>>>
>>>  static ssize_t max_freq_store(struct device *dev, struct device_attribute *attr,
>>> @@ -1162,7 +1169,14 @@ static ssize_t max_freq_store(struct device *dev, struct device_attribute *attr,
>>>  static ssize_t max_freq_show(struct device *dev, struct device_attribute *attr,
>>>                            char *buf)
>>>  {
>>> -     return sprintf(buf, "%lu\n", to_devfreq(dev)->max_freq);
>>> +     struct devfreq *df = to_devfreq(dev);
>>> +     unsigned long max_freq = to_devfreq(dev)->max_freq;
>>> +     unsigned long available_max_freq = find_available_max_freq(df);
>>> +
>>> +     if (available_max_freq != 0 && max_freq > available_max_freq)
>>> +             max_freq = available_max_freq;
>>
>> similar here.
> 
> ditto.
> 
>>
>>> +
>>> +     return sprintf(buf, "%lu\n", max_freq);
>>>  }
>>>  static DEVICE_ATTR_RW(max_freq);
> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics