linux-kernel - Re: [PATCH 07/11] PM / devfreq: check get_dev

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Date:   Wed, 10 Mar 2021 10:56:18 +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 07/11] PM / devfreq: check get_dev_status before start monitor

On Wed, Mar 10, 2021 at 12:12 AM Chanwoo Choi <cwchoi00@...il.com> wrote:
>
> On 21. 3. 10. 오전 12:58, Chanwoo Choi wrote:
> > On 21. 3. 9. 오후 9:58, Dong Aisheng wrote:
> >> The devfreq monitor depends on the device to provide load information
> >> by .get_dev_status() to calculate the next target freq.
> >>
> >> And this will cause changing governor to simple ondemand fail
> >> if device can't support.
> >>
> >> Signed-off-by: Dong Aisheng <aisheng.dong@....com>
> >> ---
> >>   drivers/devfreq/devfreq.c                 | 10 +++++++---
> >>   drivers/devfreq/governor.h                |  2 +-
> >>   drivers/devfreq/governor_simpleondemand.c |  3 +--
> >>   3 files changed, 9 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> >> index 7231fe6862a2..d1787b6c7d7c 100644
> >> --- a/drivers/devfreq/devfreq.c
> >> +++ b/drivers/devfreq/devfreq.c
> >> @@ -482,10 +482,13 @@ static void devfreq_monitor(struct work_struct
> >> *work)
> >>    * to be called from governor in response to DEVFREQ_GOV_START
> >>    * event when device is added to devfreq framework.
> >>    */
> >> -void devfreq_monitor_start(struct devfreq *devfreq)
> >> +int devfreq_monitor_start(struct devfreq *devfreq)
> >>   {
> >>       if (IS_SUPPORTED_FLAG(devfreq->governor->flags, IRQ_DRIVEN))
> >> -        return;
> >> +        return 0;
> >> +
> >> +    if (!devfreq->profile->get_dev_status)
> >> +        return -EINVAL;
>
> Again, I think that get_dev_status is not used for all governors.
> So that it cause the governor start fail. Don't check whether
> .get_dev_status is NULL or not.
>

I'm not quite understand your point.
it is used by governor_simpleondemand.c and tegra_devfreq_governor.
get_target_freq -> devfreq_update_stats -> get_dev_status

Without checking, device can switch to ondemand governor if it does not support.

Am i missed something?

Regards
Aisheng

> >>       switch (devfreq->profile->timer) {
> >>       case DEVFREQ_TIMER_DEFERRABLE:
> >> @@ -495,12 +498,13 @@ void devfreq_monitor_start(struct devfreq *devfreq)
> >>           INIT_DELAYED_WORK(&devfreq->work, devfreq_monitor);
> >>           break;
> >>       default:
> >> -        return;
> >> +        return -EINVAL;
> >>       }
> >>       if (devfreq->profile->polling_ms)
> >>           queue_delayed_work(devfreq_wq, &devfreq->work,
> >>               msecs_to_jiffies(devfreq->profile->polling_ms));
> >> +    return 0;
> >>   }
> >>   EXPORT_SYMBOL(devfreq_monitor_start);
> >> diff --git a/drivers/devfreq/governor.h b/drivers/devfreq/governor.h
> >> index 5cee3f64fe2b..31af6d072a10 100644
> >> --- a/drivers/devfreq/governor.h
> >> +++ b/drivers/devfreq/governor.h
> >> @@ -75,7 +75,7 @@ struct devfreq_governor {
> >>                   unsigned int event, void *data);
> >>   };
> >> -void devfreq_monitor_start(struct devfreq *devfreq);
> >> +int devfreq_monitor_start(struct devfreq *devfreq);
> >>   void devfreq_monitor_stop(struct devfreq *devfreq);
> >>   void devfreq_monitor_suspend(struct devfreq *devfreq);
> >>   void devfreq_monitor_resume(struct devfreq *devfreq);
> >> diff --git a/drivers/devfreq/governor_simpleondemand.c
> >> b/drivers/devfreq/governor_simpleondemand.c
> >> index d57b82a2b570..ea287b57cbf3 100644
> >> --- a/drivers/devfreq/governor_simpleondemand.c
> >> +++ b/drivers/devfreq/governor_simpleondemand.c
> >> @@ -89,8 +89,7 @@ static int devfreq_simple_ondemand_handler(struct
> >> devfreq *devfreq,
> >>   {
> >>       switch (event) {
> >>       case DEVFREQ_GOV_START:
> >> -        devfreq_monitor_start(devfreq);
> >> -        break;
> >> +        return devfreq_monitor_start(devfreq);
> >>       case DEVFREQ_GOV_STOP:
> >>           devfreq_monitor_stop(devfreq);
> >>
> >
> > Need to handle the all points of devfreq_monitor_start() usage.
> > please check the tegra30-devfreq.c for this update.
> >
> > $ grep -rn "devfreq_monitor_start" drivers/
> > drivers/devfreq/governor_simpleondemand.c:92:
> > devfreq_monitor_start(devfreq);
> > drivers/devfreq/tegra30-devfreq.c:744:
> > devfreq_monitor_start(devfreq);
> > ......
> >
>
>
> --
> Best Regards,
> Samsung Electronics
> Chanwoo Choi