linux-kernel - Re: Multiple regulators for one device [was drm/panfrost: add devfreq regulator support]

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Message-ID: <CAJiuCceECTKqTecq5KGayzNqOvQfOctR8RqnncKU66ieU7hH1w@mail.gmail.com>
Date:   Sun, 19 Apr 2020 11:25:08 +0200
From:   Clément Péron <peron.clem@...il.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Steven Price <steven.price@....com>,
        Mark Brown <broonie@...nel.org>, Nishanth Menon <nm@...com>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Viresh Kumar <vireshk@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>
Subject: Re: Multiple regulators for one device [was drm/panfrost: add devfreq
 regulator support]

Hi,

On Fri, 17 Apr 2020 at 14:33, Clément Péron <peron.clem@...il.com> wrote:
>
> Hi Robin,
>
> On Fri, 17 Apr 2020 at 13:10, Robin Murphy <robin.murphy@....com> wrote:
> >
> > On 2020-04-16 2:42 pm, Steven Price wrote:
> > [...]
> > > Perhaps a better approach would be for Panfrost to hand over the struct
> > > regulator objects it has already got to the OPP framework. I.e. open
> > > code dev_pm_opp_set_regulators(), but instead of calling
> > > regulator_get_optional() simply populate the regulators we already have?

Just saw that a Lima devfreq[0] has been also introduced with I think
exactly the same logic.

Is this something that hasn't been triggered by Maintainer or I am
missing something?

I will backport some remarks made on the lima devfreq to improve panfrost one.
They are almost identical.

Regards,
Clement

0: https://cgit.freedesktop.org/drm-misc/commit/?id=1996970773a323533e1cc1b6b97f00a95d675f32

> > >
> > > The other benefit of that is it would provide a clear hand-over of
> > > responsibility between Panfrost handling it's own regulators and the OPP
> > > framework picking up the work. The disadvantage is that Panfrost would
> > > have to track whether the regulators have been handed over or not.
> >
> > Sounds like the most logical thing to do is to shuffle things around so
> > we start by trying to set up an OPP table, then fall back to explicitly
> > claiming clocks and regulators if necessary. Then we can easily make the
> > devfreq decision later in probe based on how that turned out.
>
> Ok I will propose a new serie with this behavior,
>
> Thanks
> Clement
>
> >
> > Robin.