linux-kernel - Re: [PATCH] PCI/PM: Prevent runtime suspend before devices are fully initialized

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Message-ID: <CAJZ5v0gbH-S-vQ+rBb6zNE77_pN7n_L0g+LFUmUxontx1xrPZQ@mail.gmail.com>
Date: Tue, 21 Oct 2025 20:56:30 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Brian Norris <briannorris@...omium.org>
Cc: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Lukas Wunner <lukas@...ner.de>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	LKML <linux-kernel@...r.kernel.org>, linux-pm@...r.kernel.org, 
	linux-pci@...r.kernel.org
Subject: Re: [PATCH] PCI/PM: Prevent runtime suspend before devices are fully initialized

On Tue, Oct 21, 2025 at 8:27 PM Brian Norris <briannorris@...omium.org> wrote:
>
> On Tue, Oct 21, 2025 at 04:18:54PM +0300, Ilpo Järvinen wrote:
> > On Tue, 21 Oct 2025, Rafael J. Wysocki wrote:
> > > So the purpose of this "forbid" call in pci_pm_init() is to "block"
> > > runtime PM for PCI devices by default, but allow user space to
> > > "unblock" it later.
> > >
> > > Would adding a comment to that effect next to that call be useful?
> >
> > It would be useful to improve the wording in PM documentation which is too
> > ambiguous. I suggest changing this:
> >
> > "void pm_runtime_forbid(struct device *dev);
> >
> > unset the power.runtime_auto flag for the device and increase its
> > usage counter (used by the /sys/devices/.../power/control interface to
> > effectively prevent the device from being power managed at run time).
> >
> > to:
> >
> > "... (used to prevent the device from being power managed at run time
> > until pm_runtime_allow() or /sys/devices/.../power/control interface
> > allows it)."
>
> Looks like a good change to me, even if just scratching the surface. If
> this goes in a patch, you can add my:
>
> Reviewed-by: Brian Norris <briannorris@...omium.org>
>
> A separate problem that sorta stopped me from trying to rewrite some of
> the Documentation/ is that we have both
> Documentation/power/runtime_pm.rst and kerneldoc in
> include/linux/pm_runtime.h + drivers/base/power/runtime.c. It doesn't
> feel great having separate variations of the same API docs.
>
> But hey, I shouldn't let "perfect" be the enemy of progress.

Documentation/power/runtime_pm.rst is generally outdated.

There was a plan to replace it with a new document mostly constructed
from pm_runtime.h and pm_runtime.c kerneldocs, but those also require
some work.

I would rather remove the reference to pm_runtime_forbid() from
Documentation/power/runtime_pm.rst entirely and make the other
documentation pieces describe it properly.