linux-kernel - Re: [PATCH v3 4/5] cpufreq: apple-soc: Add new driver to control Apple SoC CPU P-states

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Date:   Mon, 14 Nov 2022 12:21:16 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Hector Martin <marcan@...can.st>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Marc Zyngier <maz@...nel.org>,
        Mark Kettenis <mark.kettenis@...all.nl>, asahi@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/5] cpufreq: apple-soc: Add new driver to control
 Apple SoC CPU P-states

On 09-11-22, 21:36, Hector Martin wrote:
> On 02/11/2022 15.18, Viresh Kumar wrote:
> >> +	ret = dev_pm_opp_set_sharing_cpus(cpu_dev, policy->cpus);
> > 
> > Why do you need this ? The OPP core should be able to find this
> > information by itself in your case AFAIU. The OPP core will refer
> > "operating-points-v2 = <&pcluster_opp>" and find that the cores are
> > related.
> 
> We have multiple clusters sharing an OPP table (e.g. the M1 Ultra has 2
> e-cluster and 4 p-clusters, and duplicating OPP tables seems very
> silly), so this is necessary to tell it about the subset of cores
> sharing a table that are actually one domain.

The cluster sharing information is already part of the OPP tables, "opp-shared"
property. Platforms like scpi needed this because they didn't have the OPP table
in DT and so no way to find out the relation of the CPUs.

See how drivers/cpufreq/mediatek-cpufreq.c has done this.
dev_pm_opp_of_get_sharing_cpus() followed by dev_pm_opp_of_cpumask_add_table().

-- 
viresh