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Subject: Re: [PATCH 07/11] PM / devfreq: check get_dev_status before start
 monitor
To:     Dong Aisheng <dongas86@gmail.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>
From:   Chanwoo Choi <cw00.choi@samsung.com>
Organization: Samsung Electronics
Message-ID: <b5a3ee55-0c71-a0ca-b03f-3b6790f3d2f4@samsung.com>
Date:   Thu, 11 Mar 2021 16:10:47 +0900
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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> wrote:
>>
>> 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.
> 
> 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. So on this version,
don't add the this conditional statement on this function

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

> 
> Regards
> Aisheng
> 
>>
>>>
>>> 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
> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics