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

From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Lukasz Luba <lukasz.luba@arm.com>
Cc: rjw@rjwysocki.net, linux-kernel@vger.kernel.org,
	linux-pm@vger.kernel.org, linux-doc@vger.kernel.org,
	devicetree@vger.kernel.org, robh+dt@kernel.org, amitk@kernel.org,
	corbet@lwn.net, Dietmar.Eggemann@arm.com, qperret@google.com,
	dianders@chromium.org, mka@chromium.org, rnayak@codeaurora.org
Subject: Re: [PATCH v2 0/3] Clarify abstract scale usage for power values in Energy Model, EAS and IPA
Date: Thu, 15 Oct 2020 12:21:55 +0200	[thread overview]
Message-ID: <00ceec64-3273-bb4a-6f38-22de8d877ab5@linaro.org> (raw)
In-Reply-To: <3e3dd42c-48ac-7267-45c5-ca88205611bd@arm.com>

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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