linux-kernel - Re: [PATCH 1/2] OPP: Use _set_opp

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Message-ID: <20231025065458.z3klmhahrcqh6qyw@vireshk-i7>
Date:   Wed, 25 Oct 2023 12:24:58 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Stephan Gerhold <stephan.gerhold@...nkonzept.com>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] OPP: Use _set_opp_level() for single genpd case

On 19-10-23, 13:16, Ulf Hansson wrote:
> On Thu, 19 Oct 2023 at 12:22, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > +static int _link_required_opps(struct dev_pm_opp *opp, struct opp_table *opp_table,
> >                                struct opp_table *required_table, int index)
> >  {
> >         struct device_node *np;
> > @@ -314,6 +314,25 @@ static int _link_required_opps(struct dev_pm_opp *opp,
> >                 return -ENODEV;
> >         }
> >
> > +       /*
> > +        * There are two genpd (as required-opp) cases that we need to handle,
> > +        * devices with a single genpd and ones with multiple genpds.
> > +        *
> > +        * The single genpd case requires special handling as we need to use the
> > +        * same `dev` structure (instead of a virtual one provided by genpd
> > +        * core) for setting the performance state. Lets treat this as a case
> > +        * where the OPP's level is directly available without required genpd
> > +        * link in the DT.
> > +        *
> > +        * Just update the `level` with the right value, which
> > +        * dev_pm_opp_set_opp() will take care of in the normal path itself.
> > +        */
> > +       if (required_table->is_genpd && opp_table->required_opp_count == 1 &&
> > +           !opp_table->genpd_virt_devs) {
> > +               if (!WARN_ON(opp->level))
> 
> Hmm. Doesn't this introduce an unnecessary limitation?
> 
> An opp node that has a required-opps phande, may have "opp-hz",
> "opp-microvolt", etc. Why would we not allow the "opp-level" to be
> used too?

Coming back to this, why would we ever want a device to have "opp-level" and
"required-opp" (set to genpd's table) ? That would mean we will call:

dev_pm_domain_set_performance_state() twice to set different level values.

And so it should be safe to force that if required-opp table is set to a genpd,
then opp-level shouldn't be set. Maybe we should fail in that case, which isn't
happening currently.

-- 
viresh