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

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Date:   Wed, 11 Oct 2017 21:57:10 +0900
From:   Chanwoo Choi <cwchoi00@...il.com>
To:     "myungjoo.ham@...sung.com" <myungjoo.ham@...sung.com>
Cc:     Chanwoo Choi <cw00.choi@...sung.com>,
        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 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.

>
>> +             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