linux-kernel - Re: [PATCH v3 2/5] devfreq: add support for suspend/resume of a devfreq device

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Date:   Thu, 06 Dec 2018 10:17:52 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Lukasz Luba <l.luba@...tner.samsung.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org
Cc:     tjakobi@...h.uni-bielefeld.de, myungjoo.ham@...sung.com,
        kyungmin.park@...sung.com, rjw@...ysocki.net, len.brown@...el.com,
        pavel@....cz, gregkh@...uxfoundation.org, keescook@...omium.org,
        anton@...msg.org, ccross@...roid.com, tony.luck@...el.com,
        robh+dt@...nel.org, mark.rutland@....com, kgene@...nel.org,
        krzk@...nel.org, m.szyprowski@...sung.com, b.zolnierkie@...sung.com
Subject: Re: [PATCH v3 2/5] devfreq: add support for suspend/resume of a
 devfreq device

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@...h.uni-bielefeld.de>
> Suggested-by: Chanwoo Choi <cw00.choi@...sung.com>
> Signed-off-by: Lukasz Luba <l.luba@...tner.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@...sung.com>

> 
> 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;
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics