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

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Message-id: <5BF61B3A.9050402@samsung.com>
Date:   Thu, 22 Nov 2018 11:58:02 +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 3/6] devfreq: add support for suspend/resume of a
 devfreq device

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@...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 | 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.

> +        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.

> +		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.


> +	}
> +
> +        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.

> +        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.

> +        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.

> +		if (ret)
> +			return ret;
> +	}
> +
>  	if (!devfreq->governor)
>  		return 0;
>  
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics