linux-kernel - Re: [PATCH 2/2] cpufreq: scmi: Update Energy Model with allowed performance limits

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Message-ID: <780caf10-964c-4a5b-8333-b448e9cbab4b@arm.com>
Date: Mon, 22 Apr 2024 15:11:52 +0200
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: Lukasz Luba <lukasz.luba@....com>, linux-kernel@...r.kernel.org,
 linux-pm@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org, sudeep.holla@....com,
 cristian.marussi@....com, linux-samsung-soc@...r.kernel.org,
 rafael@...nel.org, viresh.kumar@...aro.org, quic_sibis@...cinc.com
Subject: Re: [PATCH 2/2] cpufreq: scmi: Update Energy Model with allowed
 performance limits

On 03/04/2024 18:23, Lukasz Luba wrote:
> The Energy Model (EM) supports performance limits updates. Use the SCMI
> notifications to get information from FW about allowed frequency scope for
> the CPUs.

I'm slightly confused here. IMHO this doesn't seem to be related to the
"HW dependency between 'little CPUs & L3 $ in DSU' or similar" usecase.

I assumed that this usecase is rather handled via an additional
out-of-tree driver, potentially the same which updates the EM because of
temperature change (em_dev_compute_costs(), em_dev_update_perf_domain())
or chip binning (em_dev_update_chip_binning()).

What about other CPUFreq drivers registering an EM via
em_dev_register_perf_domain() or 'cpufreq_register_em_with_opp() ->
dev_pm_opp_of_register_em()'? Or is this 'limit notification' an SCMI FW
only thing?

[...]