linux-kernel - Re: [PATCH 08/11] PM / devfreq: check get_dev_status in devfreq_update

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Date:   Wed, 10 Mar 2021 11:00:09 +0800
From:   Dong Aisheng <dongas86@...il.com>
To:     Chanwoo Choi <cwchoi00@...il.com>
Cc:     Dong Aisheng <aisheng.dong@....com>,
        Linux PM <linux-pm@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        dl-linux-imx <linux-imx@....com>,
        open list <linux-kernel@...r.kernel.org>,
        myungjoo.ham@...sung.com, kyungmin.park@...sung.com,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Abel Vesa <abel.vesa@....com>
Subject: Re: [PATCH 08/11] PM / devfreq: check get_dev_status in devfreq_update_stats

On Wed, Mar 10, 2021 at 12:20 AM Chanwoo Choi <cwchoi00@...il.com> wrote:
>
> On 21. 3. 9. 오후 9:58, Dong Aisheng wrote:
> > Check .get_dev_status() in devfreq_update_stats in case it's abused
> > when a device does not provide it.
> >
> > Signed-off-by: Dong Aisheng <aisheng.dong@....com>
> > ---
> >   drivers/devfreq/governor.h | 3 +++
> >   1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/devfreq/governor.h b/drivers/devfreq/governor.h
> > index 31af6d072a10..67a6dbdd5d23 100644
> > --- a/drivers/devfreq/governor.h
> > +++ b/drivers/devfreq/governor.h
> > @@ -89,6 +89,9 @@ int devfreq_update_target(struct devfreq *devfreq, unsigned long freq);
> >
> >   static inline int devfreq_update_stats(struct devfreq *df)
> >   {
> > +     if (!df->profile->get_dev_status)
> > +             return -EINVAL;
> > +
>
> I'm considering the following method instead of returning the error
> when .get_dev_status is NULL.
>
>         if (!df->profile->get_dev_status) {
>                 df->last_status.total_time = 0;
>                 df->last_status.busy_time = 0;
>                 df->last_status.current_frequency = 0;
>                 return 0;
>         }

I might  suggest not cause it's meaningless for ondemand governor but
introducing confusing. Simply return error could make the life a bit easier.
does it make sense to you?

Regards
Aisheng

>
> >       return df->profile->get_dev_status(df->dev.parent, &df->last_status);
> >   }
> >   #endif /* _GOVERNOR_H */
> >
>
>
> --
> Best Regards,
> Samsung Electronics
> Chanwoo Choi