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Subject: Re: [PATCH v2 0/3] Clarify abstract scale usage for power values in
 Energy Model, EAS and IPA
To:     Quentin Perret <qperret@google.com>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Lukasz Luba <lukasz.luba@arm.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Amit Kucheria <amitk@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Dietmar Eggemann <Dietmar.Eggemann@arm.com>,
        Doug Anderson <dianders@chromium.org>,
        Matthias Kaehlcke <mka@chromium.org>,
        "Nayak, Rajendra" <rnayak@codeaurora.org>
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 <20201016121844.GA2420691@google.com>
From:   Daniel Lezcano <daniel.lezcano@linaro.org>
Message-ID: <b3c6d7a5-0564-6e84-77ff-9afe10d7ee27@linaro.org>
Date:   Fri, 16 Oct 2020 14:50:29 +0200
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On 16/10/2020 14:18, Quentin Perret wrote:
> On Friday 16 Oct 2020 at 13:48:33 (+0200), Daniel Lezcano wrote:
>> If the SCMI is returning abstract numbers, the thermal IPA governor will
>> use these numbers as a reference to mitigate the temperature at the
>> specified sustainable power which is expressed in mW in the DT. So it
>> does not work and we can not detect such conflict.
>>
>> That is why I'm advocating to keep mW for the energy model and make the
>> SCMI and DT power numbers incompatible.
> 
> I think it's fair to say SCMI-provided number should only be compared to
> other SCMI-provided numbers, so +1 on that. But what I don't understand
> is why specifying the EM in mW helps with that?

It is already specified in mW. I'm just saying to not add the
'scale'/'abstract'/'bogoWatt' in the documentation.

> Can we not let the providers specify the unit? 

Yes, it is possible but the provider must give the 'unit' and the energy
model must store this information along with the "power" numbers, so we
can compare apple with apple.

Today, the energy model is using the mW unit only and the providers are
not telling the 'unit', so both are missing.

Because both are missing, it does not make sense to talk about
'abstract' values in the energy model documentation until the above is
fixed.


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