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Subject: Re: [PATCH v3 2/5] 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>
Message-ID: <d64d50db-375d-5fd5-5938-dcd0341ef2d7@partner.samsung.com>
Date:   Thu, 6 Dec 2018 11:13:58 +0100
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Hi Chanwoo,

On 12/6/18 2:17 AM, Chanwoo Choi wrote:
> Hi Lukasz,
> 
> On 2018년 12월 05일 20:05, Lukasz Luba wrote:
>> The patch prepares devfreq device for handling suspend/resume
>> functionality. The new fields will store needed information during this
>> process. Devfreq framework handles opp-suspend DT entry and there is no
>> need of modyfications in the drivers code. It uses atomic variables to
>> make sure no race condition affects the process.
>>
>> 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 | 47 +++++++++++++++++++++++++++++++++++++++++------
>>   include/linux/devfreq.h   |  7 +++++++
>>   2 files changed, 48 insertions(+), 6 deletions(-)
> 
> Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Thank you for the review and comments for the whole patch series.

Regards,
Lukasz

> 
>>
>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>> index a9fd61b..46517b6 100644
>> --- a/drivers/devfreq/devfreq.c
>> +++ b/drivers/devfreq/devfreq.c
>> @@ -316,6 +316,10 @@ static int devfreq_set_target(struct devfreq *devfreq, unsigned long new_freq,
>>   			"Couldn't update frequency transition information.\n");
>>   
>>   	devfreq->previous_freq = new_freq;
>> +
>> +	if (devfreq->suspend_freq)
>> +		devfreq->resume_freq = cur_freq;
>> +
>>   	return err;
>>   }
>>   
>> @@ -667,6 +671,9 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>   	}
>>   	devfreq->max_freq = devfreq->scaling_max_freq;
>>   
>> +	devfreq->suspend_freq = dev_pm_opp_get_suspend_opp_freq(dev);
>> +	atomic_set(&devfreq->suspend_count, 0);
>> +
>>   	dev_set_name(&devfreq->dev, "devfreq%d",
>>   				atomic_inc_return(&devfreq_no));
>>   	err = device_register(&devfreq->dev);
>> @@ -867,14 +874,28 @@ EXPORT_SYMBOL(devm_devfreq_remove_device);
>>    */
>>   int devfreq_suspend_device(struct devfreq *devfreq)
>>   {
>> +	int ret;
>> +
>>   	if (!devfreq)
>>   		return -EINVAL;
>>   
>> -	if (!devfreq->governor)
>> +	if (atomic_inc_return(&devfreq->suspend_count) > 1)
>>   		return 0;
>>   
>> -	return devfreq->governor->event_handler(devfreq,
>> -				DEVFREQ_GOV_SUSPEND, NULL);
>> +	if (devfreq->governor) {
>> +		ret = devfreq->governor->event_handler(devfreq,
>> +					DEVFREQ_GOV_SUSPEND, NULL);
>> +		if (ret)
>> +			return ret;
>> +	}
>> +
>> +	if (devfreq->suspend_freq) {
>> +		ret = devfreq_set_target(devfreq, devfreq->suspend_freq, 0);
>> +		if (ret)
>> +			return ret;
>> +	}
>> +
>> +	return 0;
>>   }
>>   EXPORT_SYMBOL(devfreq_suspend_device);
>>   
>> @@ -888,14 +909,28 @@ EXPORT_SYMBOL(devfreq_suspend_device);
>>    */
>>   int devfreq_resume_device(struct devfreq *devfreq)
>>   {
>> +	int ret;
>> +
>>   	if (!devfreq)
>>   		return -EINVAL;
>>   
>> -	if (!devfreq->governor)
>> +	if (atomic_dec_return(&devfreq->suspend_count) >= 1)
>>   		return 0;
>>   
>> -	return devfreq->governor->event_handler(devfreq,
>> -				DEVFREQ_GOV_RESUME, NULL);
>> +	if (devfreq->resume_freq) {
>> +		ret = devfreq_set_target(devfreq, devfreq->resume_freq, 0);
>> +		if (ret)
>> +			return ret;
>> +	}
>> +
>> +	if (devfreq->governor) {
>> +		ret = devfreq->governor->event_handler(devfreq,
>> +					DEVFREQ_GOV_RESUME, NULL);
>> +		if (ret)
>> +			return ret;
>> +	}
>> +
>> +	return 0;
>>   }
>>   EXPORT_SYMBOL(devfreq_resume_device);
>>   
>> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
>> index e4963b0..d985199 100644
>> --- a/include/linux/devfreq.h
>> +++ b/include/linux/devfreq.h
>> @@ -131,6 +131,9 @@ struct devfreq_dev_profile {
>>    * @scaling_min_freq:	Limit minimum frequency requested by OPP interface
>>    * @scaling_max_freq:	Limit maximum frequency requested by OPP interface
>>    * @stop_polling:	 devfreq polling status of a device.
>> + * @suspend_freq:	 frequency of a device set during suspend phase.
>> + * @resume_freq:	 frequency of a device set in resume phase.
>> + * @suspend_count:	 suspend requests counter for a device.
>>    * @total_trans:	Number of devfreq transitions
>>    * @trans_table:	Statistics of devfreq transitions
>>    * @time_in_state:	Statistics of devfreq states
>> @@ -167,6 +170,10 @@ struct devfreq {
>>   	unsigned long scaling_max_freq;
>>   	bool stop_polling;
>>   
>> +	unsigned long suspend_freq;
>> +	unsigned long resume_freq;
>> +	atomic_t suspend_count;
>> +
>>   	/* information for device frequency transition */
>>   	unsigned int total_trans;
>>   	unsigned int *trans_table;
>>
> 
>