linux-kernel - Re: [RFC/PATCH 0/5] DVFS in the OPP core

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Message-ID: <CAPDyKFrXWAzDChd3d2acQnF6GZw57+g6XeNtHo29q3i1qjidnQ@mail.gmail.com>
Date:   Fri, 8 Feb 2019 10:45:24 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Stephen Boyd <swboyd@...omium.org>,
        Graham Roff <grahamr@...eaurora.org>,
        Mike Turquette <mturquette@...libre.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        linux-serial@...r.kernel.org, linux-spi@...r.kernel.org,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Doug Anderson <dianders@...omium.org>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [RFC/PATCH 0/5] DVFS in the OPP core

On Fri, 8 Feb 2019 at 08:17, Viresh Kumar <viresh.kumar@...aro.org> 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
clk_set_rate().

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
Uffe