linux-kernel - Re: [PATCH v2 0/3] Clarify abstract scale usage for power values in Energy Model, EAS and IPA

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Date:   Thu, 15 Oct 2020 12:21:55 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     rjw@...ysocki.net, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-doc@...r.kernel.org,
        devicetree@...r.kernel.org, robh+dt@...nel.org, amitk@...nel.org,
        corbet@....net, Dietmar.Eggemann@....com, qperret@...gle.com,
        dianders@...omium.org, mka@...omium.org, rnayak@...eaurora.org
Subject: Re: [PATCH v2 0/3] Clarify abstract scale usage for power values in
 Energy Model, EAS and IPA

On 15/10/2020 11:00, Lukasz Luba wrote:

[ ... ]

>> There is the SCMI and the DT. Because there are two sources where it is
>> impossible to know if they are using the same units, we are stuck to
>> ensure a consistency for the kernel.
>>
>> The platform should use:
>>   - the SCMI only (scaled or real)
>>   - the DT only (real)
>>   [ - the firmware file only (scaled or real) ]
>>
> 
> Do you mean by SCMI - registration using em_dev_register_perf_domain() ?

It was high level description, but yes, I guess it is the case.

>> As it is not possible to know if they are scaled or real, there is no
>> choice except making them mutually exclusive.
> 
> So you propose a bit more restriction in registration EM, to not get
> lost in the future. I also have these doubts. Let's consider it and
> maybe agree.
> 
> I've recommended Qcom to use em_dev_register_perf_domain() when they
> have this obfuscated power values. Then any developer in the future
> who wants to add EM for a new device on that platform, should use the
> em_dev_register_perf_domain().
> 
> In this case the flag in EM that you have proposed makes sense.
> We probably need an argument 'bool abstract_scale' in the
> em_dev_register_perf_domain(..., bool abstract_scale)
> as a source of information.

I was suggesting to add a flag to the em_perf_domain structure giving
the source of the power numbers.

So if the IPA is having the 'sustainable-power' set in DT but the
em_perf_domain is flagged with power number coming from SCMI, then they
will be incompatible, the thermal zone will fail to register.


> We would allow to co-exist em_dev_register_perf_domain(..., false)
> with dev_pm_opp_of_register_em() EM devices.
> 
> Is it make sense?

Well, it does not change my opinion. We should assume the energy model
is always milliwatts. If the SoC vendors find a way to get around with
bogoWatts, then good to them and up to them to deal with in the future.


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