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

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Message-ID: <740a4f0e-ee41-1e14-7b06-ab0202fd1e9f@samsung.com>
Date:   Thu, 11 Mar 2021 16:01:21 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Dong Aisheng <dongas86@...il.com>,
        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,
        Abel Vesa <abel.vesa@....com>
Subject: Re: [PATCH 08/11] PM / devfreq: check get_dev_status in
 devfreq_update_stats

On 3/10/21 12:00 PM, Dong Aisheng wrote:
> 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?

Actually, I considered the some corner case as following:
We can see the simple_ondemand governor through available_governors
even if the devfreq driver doesn't implement the .get_dev_status.
In this corner case, My intention tried to prevent the error
on this case. But, actually, it is different issue. I'll fix
this issue when get_dev_status is NULL, don't show the
simple_ondemand governor name through available_governors
on other patch.

And I applied it. Thanks.

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


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics