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From:   Dong Aisheng <dongas86@gmail.com>
Date:   Fri, 12 Mar 2021 18:57:14 +0800
Message-ID: <CAA+hA=Q0M0bTf0VLjNmf23HqFn4Unk0h4BN-mEQXb1LkZLV=NQ@mail.gmail.com>
Subject: Re: [PATCH 07/11] PM / devfreq: check get_dev_status before start monitor
To:     Chanwoo Choi <cw00.choi@samsung.com>
Cc:     Chanwoo Choi <cwchoi00@gmail.com>,
        Dong Aisheng <aisheng.dong@nxp.com>,
        Linux PM <linux-pm@vger.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@lists.infradead.org>,
        Sascha Hauer <kernel@pengutronix.de>,
        Shawn Guo <shawnguo@kernel.org>,
        dl-linux-imx <linux-imx@nxp.com>,
        open list <linux-kernel@vger.kernel.org>,
        myungjoo.ham@samsung.com, kyungmin.park@samsung.com,
        Abel Vesa <abel.vesa@nxp.com>
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On Thu, Mar 11, 2021 at 2:54 PM Chanwoo Choi <cw00.choi@samsung.com> wrote:
>
> On 3/10/21 1:56 PM, Dong Aisheng wrote:
> > On Wed, Mar 10, 2021 at 11:08 AM Chanwoo Choi <cw00.choi@samsung.com> w=
rote:
> >>
> >> On 3/10/21 11:56 AM, Dong Aisheng wrote:
> >>> On Wed, Mar 10, 2021 at 12:12 AM Chanwoo Choi <cwchoi00@gmail.com> wr=
ote:
> >>>>
> >>>> On 21. 3. 10. =EC=98=A4=EC=A0=84 12:58, Chanwoo Choi wrote:
> >>>>> On 21. 3. 9. =EC=98=A4=ED=9B=84 9:58, Dong Aisheng wrote:
> >>>>>> The devfreq monitor depends on the device to provide load informat=
ion
> >>>>>> 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@nxp.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_stru=
ct
> >>>>>> *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
> >>
> >> The devfreq can add the new governor by anyone.
> >> So these functions like devfreq_monitor_* have to support
> >> the governors and also must support the governor to be added
> >> in the future.
> >
> > Yes, but devfreq_monitor_* is only used by polling mode, right?
> > The governor using it has to implement get_dev_status unless
> > there's an exception in the future.
> >
> > Currently this patch wants to address the issue that user can switch
> > to ondemand governor (polling mode) by sysfs even devices does
> > not support it (no get_dev_status implemented).
>
> As I commented, I'll fix this issue. If devfreq driver doesn't implement
> the .get_dev_status, don't show it via available_governors. I think that
> it is fundamental solution to fix this issue.

Sounds good

> So on this version,
> don't add the this conditional statement on this function
>

Almost all this patch did is adding a checking for get_dev_status.
So do you mean drop this patch?
I wonder it's still a necessary checking to explicitly tell devfreq monitor
users that get_dev_status is needed during governor startup.

> And on next version, please use the capital letter for first character
> on patch title as following:
>
> - PM / devfreq: Check get_dev_status before start monitor
>

Okay to me.
Thanks for the suggestion.

Regards
Aisheng

> >
> > Regards
> > Aisheng
> >
> >>
> >>>
> >>> Without checking, device can switch to ondemand governor if it does n=
ot 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 *d=
evfreq)
> >>>>>>           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(struc=
t
> >>>>>> 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
> >>>
> >>>
> >>
> >>
> >> --
> >> Best Regards,
> >> Chanwoo Choi
> >> Samsung Electronics
> >
> >
>
>
> --
> Best Regards,
> Chanwoo Choi
> Samsung Electronics