linux-kernel - Re: [PATCH v3 2/2] PM / devfreq: Add governor attribute flag for specifc sysfs nodes

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Date:   Mon, 19 Oct 2020 12:55:58 +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 2/2] PM / devfreq: Add governor attribute flag for
 specifc sysfs nodes

On 10/19/20 9:38 AM, Dmitry Osipenko wrote:
> ...
>> diff --git a/Documentation/ABI/testing/sysfs-class-devfreq b/Documentation/ABI/testing/sysfs-class-devfreq
>> index deefffb3bbe4..67af3f31e17c 100644
>> --- a/Documentation/ABI/testing/sysfs-class-devfreq
>> +++ b/Documentation/ABI/testing/sysfs-class-devfreq
>> @@ -37,20 +37,6 @@ Description:
>>  		The /sys/class/devfreq/.../target_freq shows the next governor
>>  		predicted target frequency of the corresponding devfreq object.
>>  
>> -What:		/sys/class/devfreq/.../polling_interval
>> -Date:		September 2011
>> -Contact:	MyungJoo Ham <myungjoo.ham@...sung.com>
>> -Description:
>> -		The /sys/class/devfreq/.../polling_interval shows and sets
>> -		the requested polling interval of the corresponding devfreq
>> -		object. The values are represented in ms. If the value is
>> -		less than 1 jiffy, it is considered to be 0, which means
>> -		no polling. This value is meaningless if the governor is
>> -		not polling; thus. If the governor is not using
>> -		devfreq-provided central polling
>> -		(/sys/class/devfreq/.../central_polling is 0), this value
>> -		may be useless.
>> -
>>  What:		/sys/class/devfreq/.../trans_stat
>>  Date:		October 2012
>>  Contact:	MyungJoo Ham <myungjoo.ham@...sung.com>
>> @@ -65,14 +51,6 @@ Description:
>>  		as following:
>>  			echo 0 > /sys/class/devfreq/.../trans_stat
>>  
>> -What:		/sys/class/devfreq/.../userspace/set_freq
>> -Date:		September 2011
>> -Contact:	MyungJoo Ham <myungjoo.ham@...sung.com>
>> -Description:
>> -		The /sys/class/devfreq/.../userspace/set_freq shows and
>> -		sets the requested frequency for the devfreq object if
>> -		userspace governor is in effect.
>> -
>>  What:		/sys/class/devfreq/.../available_frequencies
>>  Date:		October 2012
>>  Contact:	Nishanth Menon <nm@...com>
>> @@ -109,6 +87,35 @@ Description:
>>  		The max_freq overrides min_freq because max_freq may be
>>  		used to throttle devices to avoid overheating.
>>  
>> +What:		/sys/class/devfreq/.../polling_interval
>> +Date:		September 2011
>> +Contact:	MyungJoo Ham <myungjoo.ham@...sung.com>
>> +Description:
>> +		The /sys/class/devfreq/.../polling_interval shows and sets
>> +		the requested polling interval of the corresponding devfreq
>> +		object. The values are represented in ms. If the value is
>> +		less than 1 jiffy, it is considered to be 0, which means
>> +		no polling. This value is meaningless if the governor is
>> +		not polling; thus. If the governor is not using
>> +		devfreq-provided central polling
>> +		(/sys/class/devfreq/.../central_polling is 0), this value
>> +		may be useless.
>> +
>> +		A list of governors that support the node:
>> +		- simple_ondmenad
>> +		- tegra_actmon
>> +
>> +What:		/sys/class/devfreq/.../userspace/set_freq
>> +Date:		September 2011
>> +Contact:	MyungJoo Ham <myungjoo.ham@...sung.com>
>> +Description:
>> +		The /sys/class/devfreq/.../userspace/set_freq shows and
>> +		sets the requested frequency for the devfreq object if
>> +		userspace governor is in effect.
>> +
>> +		A list of governors that support the node:
>> +		- userspace
>> +
>>  What:		/sys/class/devfreq/.../timer
>>  Date:		July 2020
>>  Contact:	Chanwoo Choi <cw00.choi@...sung.com>
>> @@ -120,3 +127,6 @@ Description:
>>  		as following:
>>  			echo deferrable > /sys/class/devfreq/.../timer
>>  			echo delayed > /sys/class/devfreq/.../timer
>> +
>> +		A list of governors that support the node:
>> +		- simple_ondemand
> 
> Hello, Chanwoo!
> 
> Could you please explain the reason of changing the doc? It looks like
> you only added the lists of governors, but is it a really useful change?
> Are you going to keep these lists up-to-date?

I think that is is useful. Because user cannot know why specific sysfs node
(like 'timer') is absence according to governor. So, in order to remove
the user confusion, better to add the information to documentation.

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics