linux-kernel - Re: [PATCH v2 09/11] cpufreq: scmi: Add support to parse domain-id using #power-domain-cells

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Message-ID: <20230721115917.lescikl75kmeqkw4@bogus>
Date:   Fri, 21 Jul 2023 12:59:17 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Cristian Marussi <cristian.marussi@....com>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>,
        Nikunj Kela <nkela@...cinc.com>,
        Prasad Sodagudi <psodagud@...cinc.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 09/11] cpufreq: scmi: Add support to parse domain-id
 using #power-domain-cells

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@....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 ?

-- 
Regards,
Sudeep