linux-kernel - Re: [External] Re: [PATCH] [RFC] Documentation: Add documentation for new platform

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Date:   Mon, 26 Oct 2020 15:55:09 -0400
From:   Mark Pearson <markpearson@...ovo.com>
To:     Hans de Goede <hdegoede@...hat.com>
CC:     <dvhart@...radead.org>, <mgross@...ux.intel.com>,
        <mario.limonciello@...l.com>, <eliadevito@...il.com>,
        <hadess@...ess.net>, <bberg@...hat.com>,
        <linux-pm@...r.kernel.org>, <linux-acpi@...r.kernel.org>,
        <platform-driver-x86@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [External] Re: [PATCH] [RFC] Documentation: Add documentation for
 new platform_profile sysfs attribute

Thanks Hans

On 26/10/2020 14:33, Hans de Goede wrote:
> Hi Mark,
> 
> Thank you for this new version.
> 
> On 10/26/20 6:44 PM, Mark Pearson wrote:
>> From: Hans de Goede <hdegoede@...hat.com>
>>
<snip>

>> +
>> +If for some reason there is no good match when mapping then a new profile-name
>> +may be added. Drivers which wish to introduce new profile-names must:
>> +1. Have very good reasons to do so.
>> +2. Add the new profile-name to this document, so that future drivers which also
>> +   have a similar problem can use the same new.
> 
> s/same new/same name/
I've read this document so many times...I'm not sure how I missed that 
one. Thanks.
> 
>> + Usually new profile-names will
>> +   be added to the "extra profile-names" section of this document. But in some
>> +   cases the set of standard profile-names may be extended.
> 
> With the change from a more generic API to this new one more targeted towards DPTF
> I would drop this part.
OK - I have some questions then related to this change, below
> 
> 
>> +
>> +What:		/sys/firmware/acpi/platform_profile_choices
>> +Date:		October 2020
>> +Contact:	Hans de Goede <hdegoede@...hat.com>
>> +Description:
>> +		Reading this file gives a space separated list of profiles
>> +		supported for this device.
>> +
>> +		Drivers must use the following standard profile-names whenever
>> +		possible:
>> +
>> +		low-power:		Emphasises low power consumption
>> +		quiet:			Offers quieter operation (lower fan
>> +					speed but with higher performance and
>> +					temperatures then seen in low-power
> 
> I think the description here is a bit too specific, this may cause userspace
> to have expectations which are not necessary true. I would describe this as
> just:
> 
> 		quiet:			Emphasises quieter operation
> 
Agreed. I'll update

>> +		balanced:		Balance between low power consumption
>> +					and performance
>> +		performance:		Emphasises performance (and may lead to
>> +					higher temperatures and fan speeds)
>> +
>> +		Userspace may expect drivers to offer at least several of these
>> +		standard profile-names! If none of the above are a good match
>> +		for some of the drivers profiles, then drivers may use one of
>> +		these extra profile-names:
>> +		<reserved for future use>
>> +
If we remove the extra profile-names section above then I think it 
should be removed here too. If someone wants to add a new 'mode' then it 
would be added to the list of 'standard names', and becomes a new 
option. Wanted to check I'm not missing something important.

>> +What:		/sys/firmware/acpi/platform_profile
>> +Date:		October 2020
>> +Contact:	Hans de Goede <hdegoede@...hat.com>
>> +Description:
>> +		Reading this file gives the current selected profile for this
>> +		device. Writing this file with one of the strings from
>> +		available_profiles changes the profile to the new value.
> 
> The part about custom profiles below may be dropped. That was intended for use
> with e.g. GPUs but since this now strictly is a system-level profile API, the
> part below can be dropped now.
Agreed
> 
> 
>> +
>> +		Reading this file may also return "custom". This is intended for
>> +		drivers which have and export multiple knobs. Such drivers may
>> +		very well still want to offer a set of profiles for easy of use
>> +		and to be able to offer a consistent standard API (this API) to
>> +		userspace for configuring their performance. The "custom" value
>> +		is intended for when ai user has directly configured the knobs
>> +		(through e.g. some advanced control-panel for a GPU) and the
>> +		knob values do not match any of the presets represented by the
>> +		platform-profiles. In this case writing this file will
>> +		override the modifications and restore the selected presets.
>> +
>>
> 
> Regards,
> 
> Hans
> 
Thanks!
mark