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From:   Ulf Hansson <ulf.hansson@linaro.org>
Date:   Wed, 26 Jul 2023 13:31:19 +0200
Message-ID: <CAPDyKFr6oduyihOd7u6UW3RJAJr=a3mT8Dw9GtryhK4+SRK_wg@mail.gmail.com>
Subject: Re: [PATCH v2 09/11] cpufreq: scmi: Add support to parse domain-id
 using #power-domain-cells
To:     Sudeep Holla <sudeep.holla@arm.com>
Cc:     Cristian Marussi <cristian.marussi@arm.com>,
        Viresh Kumar <vireshk@kernel.org>, Nishanth Menon <nm@ti.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Nikunj Kela <nkela@quicinc.com>,
        Prasad Sodagudi <psodagud@quicinc.com>,
        Alexandre Torgue <alexandre.torgue@foss.st.com>,
        linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org
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On Fri, 21 Jul 2023 at 13:59, Sudeep Holla <sudeep.holla@arm.com> wrote:
>
> On Fri, Jul 21, 2023 at 01:52:17PM +0200, Ulf Hansson wrote:
> > On Wed, 19 Jul 2023 at 17:24, Sudeep Holla <sudeep.holla@arm.com> wrote:
> > >
> > > On Thu, Jul 13, 2023 at 04:17:36PM +0200, Ulf Hansson wrote:
> > > > The performance domain-id can be described in DT using the power-domains
> > > > property or the clock property. The latter is already supported, so let's
> > > > add support for the power-domains too.
> > > >
> > >
> > > How is this supposed to work for the CPUs ? The CPU power domains are
> > > generally PSCI on most of the platforms and the one using OSI explicitly
> > > need to specify the details while ones using PC will not need to. Also they
> > > can never be performance domains too. So I am not sure if I am following this
> > > correctly.
> >
> > Your concerns are certainly correct, I completely forgot about this.
> > We need to specify what power-domain index belongs to what, by using
> > power-domain-names in DT. So a CPU node, that has both psci for power
> > and scmi for performance would then typically look like this:
> >
> > power-domains = <&CPU_PD0>, <&scmi_dvfs 4>;
> > power-domain-names = "psci", "scmi";
> >
> > I will take care of this in the next version - and thanks a lot for
> > pointing this out!
>
>
> Yes something like this will work. Just curious will this impact the idle
> paths ? By that I mean will the presence of additional domains add more
> work or will they be skipped as early as possible with just one additional
> check ?

Unless I misunderstand your concern, I don't think there is any impact
on the idle path whatsoever. This should be entirely orthogonal.

The scmi-cpufreq driver should only have to care about the
scmi-performance domain, while the cpuidle-psci driver cares only
about psci.

Did that make sense?

Kind regards
Uffe