Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 16 Oct 2020 14:09:05 +0100
From:   Quentin Perret <qperret@google.com>
To:     Daniel Lezcano <daniel.lezcano@linaro.org>
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>
Subject: Re: [PATCH v2 0/3] Clarify abstract scale usage for power values in
 Energy Model, EAS and IPA
Message-ID: <20201016130905.GA2426638@google.com>
References: <b19c1f12-b7cf-fcae-4ebb-617019effe2e@arm.com>
 <55d3fb0f-f7d8-63c5-2bdb-53eaa62380e0@linaro.org>
 <f660731e-132b-2514-f526-d7123ed3522c@arm.com>
 <d04019bd-9e85-5f3e-2a1b-66780b8df3dc@linaro.org>
 <3e3dd42c-48ac-7267-45c5-ca88205611bd@arm.com>
 <00ceec64-3273-bb4a-6f38-22de8d877ab5@linaro.org>
 <CAJZ5v0hV8fwRnADdjiiF=zapO3AE6=_W_PeOQ_WhUirCcFkgdA@mail.gmail.com>
 <e321191c-61d2-a15d-47c2-653b277984ca@linaro.org>
 <20201016121844.GA2420691@google.com>
 <b3c6d7a5-0564-6e84-77ff-9afe10d7ee27@linaro.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <b3c6d7a5-0564-6e84-77ff-9afe10d7ee27@linaro.org>
Precedence: bulk

On Friday 16 Oct 2020 at 14:50:29 (+0200), Daniel Lezcano wrote:
> 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.

Right, so that sounds like a reasonable way forward with this series.

Lukasz would you be able to re-spin this with a first patch that allows
the EM provider to specify a unit? And perhaps we could use Doug's idea
for the sustained power DT binding and allow specifying a unit
explicitly there too, so we're sure to compare apples with apples.

Thanks,
Quentin