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Subject: Re: [PATCH 07/11] PM / devfreq: check get_dev_status before start
 monitor
To:     Dong Aisheng <dongas86@gmail.com>,
        Chanwoo Choi <cwchoi00@gmail.com>
Cc:     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>
From:   Chanwoo Choi <cw00.choi@samsung.com>
Organization: Samsung Electronics
Message-ID: <31be2267-8988-f162-f5a6-6e6389bbf1fb@samsung.com>
Date:   Wed, 10 Mar 2021 12:25:31 +0900
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On 3/10/21 11:56 AM, Dong Aisheng wrote:
> On Wed, Mar 10, 2021 at 12:12 AM Chanwoo Choi <cwchoi00@gmail.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@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_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

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.

> 
> 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
> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics