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Subject: Re: [PATCH 3/6] devfreq: add support for suspend/resume of a
 devfreq device
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
From:   Lukasz Luba <l.luba@partner.samsung.com>
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Date:   Mon, 3 Dec 2018 15:05:10 +0100
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Hi Chanwoo Choi,

On 11/26/18 1:19 AM, Chanwoo Choi wrote:
> Hi Lukasz,
> 
> I add the one more comment for devfreq_resume_device()
> 
> On 2018년 11월 23일 19:01, Lukasz Luba wrote:
>> Hi Chanwoo Choi,
>>
>> On 11/23/18 12:54 AM, Chanwoo Choi wrote:
>>> 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) {
> 
> In devfreq_resume_device(), it should check the 'devfreq->resume_freq'
> instead of 'devfreq->suspend_freq'.
OK, I will fix it.

Regards,
Lukasz

> 
> 
>>>>>> +		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;
>>> 	}
>>>
>>>
>> OK, I will change the code to keep the same format.
>> Thank you for the review.
>>
>> Regards,
>> Lukasz
>>
>>
>>
> 
>