linux-kernel - Re: [PATCH 2/2] OPP/pmdomain: Fix the assignment of the required-devs

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Message-ID: <20240906061405.bz7y3erlz4v5fvvd@vireshk-i7>
Date: Fri, 6 Sep 2024 11:44:05 +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>,
	Dikshita Agarwal <quic_dikshita@...cinc.com>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <quic_kdybcio@...cinc.com>,
	Nikunj Kela <nkela@...cinc.com>,
	Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Mikko Perttunen <mperttunen@...dia.com>,
	Jonathan Hunter <jonathanh@...dia.com>,
	Stephan Gerhold <stephan@...hold.net>,
	Ilia Lin <ilia.lin@...nel.org>,
	Stanimir Varbanov <stanimir.k.varbanov@...il.com>,
	Vikash Garodia <quic_vgarodia@...cinc.com>,
	linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] OPP/pmdomain: Fix the assignment of the required-devs

On 04-09-24, 14:57, Ulf Hansson wrote:
> > Yeah, I missed that, it doesn't happen via DT but by platform code. I
> > do see problems where situation would be a bit ambiguous. Your example
> > with a minor change to your code:
> >
> >         opp_table_devA: opp-table-devA {
> >                 compatible = "operating-points-v2";
> >
> >                 opp-devA-50 {
> >                         opp-hz = /bits/ 64 <2500>;
> >                         required-opps = <&opp_pd_50, &opp_pd_51>; //corresponds to pd_perf1 and pd_perf0 (in reverse order)
> >                 };
> >                ....
> >
> >         devA {
> >                 compatible = "foo,bar";
> >                 power-domains = <&pd_perf0>, <&pd_perf1>; //both
> > pd_perf0 and pd_perf1 has OPP tables.
> >                 power-domain-names = "perf0", "perf1";
> >                 operating-points-v2 = <&opp_table_devA>;
> >         };
> >
> > Here, I don't think there is a way for us to know which genpd does
> > opp_pd_50 belongs to and to which one opp_pd_51 does.
> >
> > We solve this by sending clock_names and regulator_names in OPP
> > config structure. That gives the ordering in which required_opps are
> > present. The same needs to be done for genpd, and then genpd core
> > would be able to attach the right genpd with right required opp.
> 
> No, we don't need this for gend as $subject patch is addressing this
> problem too. Let me elaborate.
> 
> The OPP core holds the information about the devA's required-opps and
> to what OPP table each required-opps belongs to
> (opp_table->required_opp_tables[n]).
> 
> The genpd core holds the information about the allocated virtual
> devices that it creates when it attached devA to its power-domains.
> The virtual device(s) gets a genpd attached to it and that genpd also
> has an OPP table associated with it (genpd->opp_table).
> 
> By asking the OPP core to walk through the array of allocated
> required-opps for devA and to match it against a *one* of the virtual
> devices' genpd->opp_table, we can figure out at what index we should
> assign the virtual device to in the opp_table->required_devs[index].

How do we differentiate between two cases where the required-opps can
be defined as either of these:

required-opps = <&opp_pd_50, &opp_pd_51>; //corresponds to pd_perf1 and pd_perf0 (in reverse order)

OR

required-opps = <&opp_pd_51, &opp_pd_50>; //corresponds to pd_perf0 and pd_perf1

I thought this can't be fixed without some platform code telling how
the DT is really configured, i.e. order of the power domains in the
required-opps.

-- 
viresh