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

From: Chanwoo Choi <cw00.choi@samsung.com>
To: Lukasz Luba <l.luba@partner.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: Fri, 23 Nov 2018 08:54:06 +0900	[thread overview]
Message-ID: <5BF7419E.90006@samsung.com> (raw)
In-Reply-To: <cce4f194-b574-a12c-e876-f11a6f245940@partner.samsung.com>

Hi Lukasz,

I add one more comment about devfreq_resume_device().

On 2018년 11월 22일 20:00, Lukasz Luba wrote:
> 
> 
> 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().

OK.

>>
>>> +        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

If you change the devfreq_resume_device() according to my new comment,
please ignore it.

>>
>>> +        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;

Please change the code as following because you uses the following type
in the devfreq_suspend_device(). If there is any special issue, please
keep the same format in order to improve the readability. 

	if (devfreq->governor) {                                                
		ret = devfreq->governor->event_handler(devfreq,                 
				DEVFREQ_GOV_RESUME, NULL);             
		if (ret)                                                        
			return ret;                                             
	}        

>>>   
>>>
>>
>>
> 
> Regards,
> Lukasz Luba
> 
> 

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics