linux-kernel - Re: [PATCH v3 1/2] PM / devfreq: Add governor feature flag

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Date:   Mon, 19 Oct 2020 12:53:34 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Dmitry Osipenko <digetx@...il.com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org
Cc:     leonard.crestez@....com, lukasz.luba@....com,
        enric.balletbo@...labora.com, hl@...k-chips.com,
        thierry.reding@...il.com, jonathanh@...dia.com, abel.vesa@....com,
        k.konieczny@...sung.com, b.zolnierkie@...sung.com,
        chanwoo@...nel.org, myungjoo.ham@...sung.com,
        kyungmin.park@...sung.com
Subject: Re: [PATCH v3 1/2] PM / devfreq: Add governor feature flag

On 10/19/20 9:57 AM, Dmitry Osipenko wrote:
> 07.10.2020 08:07, Chanwoo Choi пишет:
>> The devfreq governor is able to have the specific flag as follows
>> in order to implement the specific feature. For example, devfreq allows
>> user to change the governors on runtime via sysfs interface.
>> But, if devfreq device uses 'passive' governor, don't allow user to change
>> the governor. For this case, define the DEVFREQ_GOV_FLAT_IMMUTABLE
> 
> s/DEVFREQ_GOV_FLAT/DEVFREQ_GOV_FLAG/
> 
> ...
>>  /**
>>   * struct devfreq_governor - Devfreq policy governor
>>   * @node:		list node - contains registered devfreq governors
>>   * @name:		Governor's name
>> - * @immutable:		Immutable flag for governor. If the value is 1,
>> - *			this governor is never changeable to other governor.
>> - * @interrupt_driven:	Devfreq core won't schedule polling work for this
>> - *			governor if value is set to 1.
>> + * @flag:		Governor's feature flag
>>   * @get_target_freq:	Returns desired operating frequency for the device.
>>   *			Basically, get_target_freq will run
>>   *			devfreq_dev_profile.get_dev_status() to get the
>> @@ -50,8 +57,7 @@ struct devfreq_governor {
>>  	struct list_head node;
>>  
>>  	const char name[DEVFREQ_NAME_LEN];
>> -	const unsigned int immutable;
>> -	const unsigned int interrupt_driven;
>> +	const u64 flag;
> A plural form of flag(s) is more common, IMO.

When need to add more feature flag, I prefer to add
the definition instead of changing the structure.
I think it is better.

> 
> It's also possible to use a single bit:1 for the struct members. Thus,
> could you please explain what are the benefits of the "flag"?

I think that anyone might add the some optional
feature. So, I used 'flag' for the extensibility.



-- 
Best Regards,
Chanwoo Choi
Samsung Electronics