linux-kernel - Re: [PATCH v2 3/3] PM: runtime: Clarify documentation when callbacks are unassigned

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Date:   Wed, 9 Jun 2021 11:45:07 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Alan Stern <stern@...land.harvard.edu>
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 v2 3/3] PM: runtime: Clarify documentation when callbacks
 are unassigned

On Tue, 8 Jun 2021 at 16:49, Alan Stern <stern@...land.harvard.edu> wrote:
>
> On Tue, Jun 08, 2021 at 04:30:48PM +0200, Ulf Hansson wrote:
> > On Tue, 8 Jun 2021 at 16:23, Alan Stern <stern@...land.harvard.edu> wrote:
> > >
> > > On Tue, Jun 08, 2021 at 11:02:50AM +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 v2:
> > > >       - Added a new patch for the updating the docs, as pointed out by Alan.
> > > >
> > > > ---
> > > >  Documentation/power/runtime_pm.rst | 8 ++++++++
> > > >  1 file changed, 8 insertions(+)
> > > >
> > > > diff --git a/Documentation/power/runtime_pm.rst b/Documentation/power/runtime_pm.rst
> > > > index 18ae21bf7f92..3d09c9fd450d 100644
> > > > --- a/Documentation/power/runtime_pm.rst
> > > > +++ b/Documentation/power/runtime_pm.rst
> > > > @@ -827,6 +827,14 @@ 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
>
> More than 80 chars.

Perhaps it's the email client that messes up the patch in some way.
This above line in the patch is 79 chars.

If you have a look at the patch in patchwork [1], you should see (I
hope) that it respects the 80 chars per line!?

>
> > > > +pm_runtime_no_callbacks() for their devices. This could be because a subset of
>
> More than 80 chars.
>
> > > > +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 manged
>
> s/manged/managed/

Thanks for spotting this, my spell checker accepted "manged". :-)

>
> > > > +through a supplier device link. For these reasons and to avoid boilerplate code
>
> More than 80 chars.
>
> > > > +in subsystems/drivers, the PM core allows runtime PM callbacks to be
> > > > +unassigned.
> > > > +
> > >
> > > You should also mention that if a callback pointer is NULL, the
> > > runtime PM core will act as though there was a callback and it
> > > returned 0.  That's an important consideration.
> >
> > Good point, let me add it.
> >
> > I send a new version of $subject patch, unless Rafael is happy to do
> > the amending when/if applying?
> >
> > >
> > > Also, notice that this file was carefully edited to make sure that
> > > none of the lines exceed 80 characters.  Your new addition should
> > > be the same.
> >
> > Absolutely, but it should be okay already, no?
>
> See above.
>
> Alan

Kind regards
Uffe

[1]
https://patchwork.kernel.org/project/linux-pm/patch/20210608090250.85256-4-ulf.hansson@linaro.org/