Re: [PATCH 3/6] devfreq: add support for suspend/resume of a devfreq device

From: Lukasz Luba <l.luba@partner.samsung.com>
To: Chanwoo Choi <cw00.choi@samsung.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-samsung-soc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-pm@vger.kernel.org, devicetree@vger.kernel.org
Cc: tjakobi@math.uni-bielefeld.de, myungjoo.ham@samsung.com,
	kyungmin.park@samsung.com, rjw@rjwysocki.net,
	len.brown@intel.com, pavel@ucw.cz, gregkh@linuxfoundation.org,
	keescook@chromium.org, anton@enomsg.org, ccross@android.com,
	tony.luck@intel.com, robh+dt@kernel.org, mark.rutland@arm.com,
	kgene@kernel.org, krzk@kernel.org, m.szyprowski@samsung.com,
	b.zolnierkie@samsung.com
Subject: Re: [PATCH 3/6] devfreq: add support for suspend/resume of a devfreq device
Date: Thu, 22 Nov 2018 12:00:45 +0100	[thread overview]
Message-ID: <cce4f194-b574-a12c-e876-f11a6f245940@partner.samsung.com> (raw)
In-Reply-To: <5BF61B3A.9050402@samsung.com>


On 11/22/18 3:58 AM, Chanwoo Choi wrote:
> On 2018년 11월 22일 03:01, Lukasz Luba wrote:
>> The patch adds support for handling suspend/resume process.
>> It uses atomic variables to make sure no race condition
>> affects the process.
>>
>> The patch draws on Tobias Jakobi's work posted ~2 years ago, who tried to
>> solve issue with devfreq device's frequency during suspend/resume.
>> During the discussion on LKML some corner cases and comments appeared
>> related to the design. This patch address them keeping in mind suggestions
>> from Chanwoo Choi.
> 
> Please remove the duplicate information about patch history.
> 
>>
>> Suggested-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
>> Suggested-by: Chanwoo Choi <cw00.choi@samsung.com>
>> Signed-off-by: Lukasz Luba <l.luba@partner.samsung.com>
>> ---
>>   drivers/devfreq/devfreq.c | 45 +++++++++++++++++++++++++++++++++++++++------
>>   1 file changed, 39 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>> index cf9c643..7e09de8 100644
>> --- a/drivers/devfreq/devfreq.c
>> +++ b/drivers/devfreq/devfreq.c
>> @@ -872,14 +872,33 @@ EXPORT_SYMBOL(devm_devfreq_remove_device);
>>    */
>>   int devfreq_suspend_device(struct devfreq *devfreq)
>>   {
>> -	if (!devfreq)
>> -		return -EINVAL;
>> +        int ret;
> 
> Move 'ret' definition under 'if (devfreq->suspend_freq) {'
> because 'ret' is used if suspend_freq isn't zero.
Not only there, 6 lines above 'ret' is used for 
devfreq->governor->event_handler().
> 
>> +        unsigned long prev_freq;
>> +        u32 flags = 0;
>> +
>> +        if (!devfreq)
>> +                return -EINVAL;
>> +
>> +        if (devfreq->governor) {
>> +		ret = devfreq->governor->event_handler(devfreq,
>> +					DEVFREQ_GOV_SUSPEND, NULL);
>> +		if (ret)
>> +			return ret;
>> +	}
>>   
>> -	if (!devfreq->governor)
>> -		return 0;
>> +	if (devfreq->suspend_freq) {
>> +		if (atomic_inc_return(&devfreq->suspend_count) > 1)
>> +			return 0;
>>   
>> -	return devfreq->governor->event_handler(devfreq,
>> -				DEVFREQ_GOV_SUSPEND, NULL);
>> +		ret = devfreq_set_target(devfreq, devfreq->suspend_freq,
>> +					 &prev_freq, flags);
> 
> Remove the 'prev_freq' parameter.
OK
> 
>> +		if (ret)
>> +			return ret;
>> +
>> +		devfreq->resume_freq = prev_freq;
> 
> As I commented on patch2, if devfreq_set_taget save the current frequency
> to 'devfreq->resume_freq', this line is not needed.
OK
> 
> 
>> +	}
>> +
>> +        return 0;
>>   }
>>   EXPORT_SYMBOL(devfreq_suspend_device);
>>   
>> @@ -893,9 +912,23 @@ EXPORT_SYMBOL(devfreq_suspend_device);
>>    */
>>   int devfreq_resume_device(struct devfreq *devfreq)
>>   {
>> +        int ret;
> 
> Move 'ret' definition under 'if (devfreq->suspend_freq) {'
> because 'ret' is used if suspend_freq isn't zero.
OK
> 
>> +        unsigned long prev_freq;
> 
> Remove prev_freq variable which is not used on this function.
> After calling devfreq_set_target, prev_freq is not used.
OK
> 
>> +        u32 flags = 0;
>> +
>>   	if (!devfreq)
>>   		return -EINVAL;
>>   
>> +	if (devfreq->suspend_freq) {
>> +		if (atomic_dec_return(&devfreq->suspend_count) >= 1)
>> +			return 0;
>> +
>> +		ret = devfreq_set_target(devfreq, devfreq->resume_freq,
>> +					 &prev_freq, flags);
> 
> Remove the 'prev_freq' parameter.
OK
> 
>> +		if (ret)
>> +			return ret;
>> +	}
>> +
>>   	if (!devfreq->governor)
>>   		return 0;
>>   
>>
> 
> 

Regards,
Lukasz Luba