linux-kernel - Re: [PATCH v4 3/3] PM: runtime: Clarify documentation when callbacks are unassigned

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Message-ID: <CAJZ5v0j30rEvGhWm7YgLPcMe53r9gyi3wrw+j+0Lm6T1p2t6Yg@mail.gmail.com>
Date:   Fri, 11 Jun 2021 19:05:39 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Alan Stern <stern@...land.harvard.edu>,
        Ulf Hansson <ulf.hansson@...aro.org>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Tony Lindgren <tony@...mide.com>,
        Kevin Hilman <khilman@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/3] PM: runtime: Clarify documentation when callbacks
 are unassigned

On Wed, Jun 9, 2021 at 4:16 PM Alan Stern <stern@...land.harvard.edu> wrote:
>
> On Wed, Jun 09, 2021 at 12:06:10PM +0200, Ulf Hansson wrote:
> > Recent changes to the PM core allows ->runtime_suspend|resume callbacks to
> > be unassigned.
> >
> > In the earlier behaviour the PM core would return -ENOSYS, when trying to
> > runtime resume a device, for example. Let's update the documentation to
> > clarify this.
> >
> > Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> > ---
> >
> > Changes in v4:
> >         - This time, really, fix spelling and further clarified the behaviour,
> >       according to comments from Alan.
> >
> > ---
> >  Documentation/power/runtime_pm.rst | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/Documentation/power/runtime_pm.rst b/Documentation/power/runtime_pm.rst
> > index 18ae21bf7f92..8a0a43811e3a 100644
> > --- a/Documentation/power/runtime_pm.rst
> > +++ b/Documentation/power/runtime_pm.rst
> > @@ -827,6 +827,15 @@ or driver about runtime power changes.  Instead, the driver for the device's
> >  parent must take responsibility for telling the device's driver when the
> >  parent's power state changes.
> >
> > +Note that, in some cases it may not be desirable for subsystems/drivers to call
> > +pm_runtime_no_callbacks() for their devices. This could be because a subset of
> > +the runtime PM callbacks needs to be implemented, a platform dependent PM
> > +domain could get attached to the device or that the device is power managed
> > +through a supplier device link. For these reasons and to avoid boilerplate code
> > +in subsystems/drivers, the PM core allows runtime PM callbacks to be
> > +unassigned. More precisely, if a callback pointer is NULL, the PM core will act
> > +as though there was a callback and it returned 0.
> > +
> >  9. Autosuspend, or automatically-delayed suspends
> >  =================================================
>
> Acked-by: Alan Stern <stern@...land.harvard.edu>

Applied as 5.14 material along with the [1-2/3] from this series.

Thanks!