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

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Date:   Tue, 27 Oct 2020 08:54:44 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Mark Pearson <markpearson@...ovo.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

Hi,

On 10/26/20 8:55 PM, Mark Pearson wrote:
> 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.

You are completely right, any references to an extra profile-names section
should be removed here too. I did intend to add that it should be removed here
too, but I forgot.


>>> +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

Regards,

Hans