linux-kernel - Re: [PATCH v6 10/10] soc: qcom: rpmhpd: Mark mx as a parent for cx

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Date:   Thu, 13 Dec 2018 17:02:43 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     swboyd@...omium.org, Rajendra Nayak <rnayak@...eaurora.org>
Cc:     Andy Gross <andy.gross@...aro.org>, Rob Herring <robh@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        David Collins <collinsd@...eaurora.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        DTML <devicetree@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 10/10] soc: qcom: rpmhpd: Mark mx as a parent for cx

On Wed, 12 Dec 2018 at 19:32, Stephen Boyd <swboyd@...omium.org> wrote:
>
> Quoting Rajendra Nayak (2018-12-11 20:13:13)
> >
> > >>> Just to make sure there are no conflicting hierarchical constraints
> > >>> between idle management and performance state management!?
> > >>>
> > >
> > > I'm not sure what idle states mean to the CX and MX domains. Would it be
> > > some sort of idle state governor attached at genpd creation time that
> > > would adjust the main SoC power rails when all devices attached are
> > > idle? Maybe I don't understand how idle states are different from
> > > performance states.
> > > My understanding is that devices using these domains would almost always
> > > expect their clk frequency and clk on/off state to decide what the
> > > performance state is, unless they need to ignore clk state because they
> > > aren't managing clks and bump up the voltage directly when the device is
> > > active. Either way, devices are actively managing the voltage they need
> > > these voltage domains to operate at by using the genpd performance
> > > states APIs.
> >
> > I am not quite sure whats the point that you are trying to make here,
> > but this is what I would expect the users of these genpds to do,
> > regardless of if they have a clk dependency or not.
> > When the device is active, vote for a performance state they need
> > then request for the genpd to be on. When they are idle, request for the
> > genpd to be turned off.
> >
>
> I believe Ulf is asking because he's proposing to make genpd idle states
> and genpd performance states orthogonal to each other. And to also make
> performance states unaffected by the on/off state of the genpd.

Yes, that's one of the reasons.

Anyway, I appreciate both of yours descriptive feedback, no further
worries from my side!

Kind regards
Uffe