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

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Date:   Fri, 8 Feb 2019 11:31:13 +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 11:05, Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 08-02-19, 10:45, Ulf Hansson wrote:
> > 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. :-)
>
> It was me. I thought you are talking about regulators and that is what
> is already managed, i.e. to work with or without regulators.
>
> > 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?
>
> Yeah, that would be a problem and hacking the OPP core may not be the
> right solution :(

I guess one simple way forward could just be to check if there is an
OPP handle/table available, then use dev_pm_opp_set_rate(). When no
OPP handle/table, use clk_set_rate() *instead*, not both.

That could work, don't you think?

Kind regards
Uffe