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Date:   Fri, 16 Oct 2020 16:55:19 +0100
From:   Quentin Perret <qperret@google.com>
To:     Doug Anderson <dianders@chromium.org>
Cc:     Daniel Lezcano <daniel.lezcano@linaro.org>,
        "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>,
        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
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On Friday 16 Oct 2020 at 07:36:03 (-0700), Doug Anderson wrote:
> The one issue that I started with, though, is that I wanted to be able
> to specify "sustainable-power" for a board in the device tree.  Unless
> you think you'll convince Rob that it's OK to provide a "units"
> property in the device tree then just adding a "units" to the API
> won't help us because you'll still be stuck mixing/matching with a
> value based in mW, right?  ...or are you suggesting that the
> board-specific value "sustainable-power" would also have to come from
> SCMI?  That would be pretty annoying.

Hmm, maybe, but that's the sanest option IMO.

We should fix the PM_EM API regardless of the DT stuff because
pretending SCMI values are mW is kinda dodgy and confusing. And for the
sustained power stuff, then yes you need this in a comparable unit. If
SCMI gives it to you then it sounds like should just use that. And if we
can make that change to the DT binding then you'll be able to specify it
there as well. But if we can't, then we just won't support mixing and
matching DT and SCMI values. So, yeah, either the EM or the sustained
power value will have to be provided some other way, to keep thing
consistent ...