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

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Message-ID: <20231025104809.qw5vk3liuffgtqk3@vireshk-i7>
Date:   Wed, 25 Oct 2023 16:18:09 +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 25-10-23, 12:40, Ulf Hansson wrote:
> On Wed, 25 Oct 2023 at 08:55, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > On 19-10-23, 13:16, Ulf Hansson wrote:
> > > On Thu, 19 Oct 2023 at 12:22, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > > > +       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.
> 
> Yes - and that would be weird, especially since the PM domain (genpd)
> is already managing the aggregation and propagation to parent domains.
> 
> I guess I got a bit confused by the commit message for patch2/2, where
> it sounded like you were striving towards introducing recursive calls
> to set OPPs. Having a closer look, I realize that isn't the case,
> which I think makes sense.
> 
> >
> > 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.
> 
> Yes, it seems better to fail earlier during the OF parsing of the
> required-opps or when adding an OPP dynamically. In that way, the
> WARN_ON above could be removed.

For now I will leave the WARN as is, will reconsider if it makes more
sense to fail and return early. And send a separate patch for that.

> That said, sorry for the noise and either way, feel free to add (for
> $subject patch):
> 
> Reviewed-by: Ulf Hansson <ulf.hansson@...aro.org>

Thanks.

-- 
viresh