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Date:   Fri, 8 Feb 2019 10:45:24 +0100
From:   Ulf Hansson <>
To:     Viresh Kumar <>
Cc:     Stephen Boyd <>,
        Graham Roff <>,
        Mike Turquette <>,
        Linux Kernel Mailing List <>,
        linux-arm-msm <>,
        Linux PM <>,,,
        Rajendra Nayak <>,
        Doug Anderson <>,
        Vincent Guittot <>
Subject: Re: [RFC/PATCH 0/5] DVFS in the OPP core

On Fri, 8 Feb 2019 at 08:17, Viresh Kumar <> wrote:
> On 07-02-19, 14:37, Ulf Hansson wrote:
> > I think we also need to consider cross SoC drivers. One SoC may have
> > both clocks and OPPs to manage, while another may have only clocks.
> We already have that case with CPUs as well and dev_pm_opp_set_rate()
> takes care of it.

I think you may have misunderstood my point. Or maybe I don't get yours. :-)

What if there is no OPP at all to use, then dev_pm_opp_set_rate() is
just a noop, right? In this scenario the driver still need to call

How do we cope with these cases?

> > Even it this may be fairly uncommon, we should consider it, before we
> > decide to fold in additional clock management, like
> > clk_prepare|unprepare() for example, behind the dev_pm_opp_set_rate()
> > API.
> >
> > The point is, the driver may need to call clk_prepare|enable()
> > anyways, unless we make that conditional depending on a DT compatible
> > string, for example. Of course, because the clock prepare/enable is
> > reference counted, there may not be a problem in practice to have both
> > the OPP and driver to deal with it.

Kind regards

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