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

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Message-ID: <aPfQmy0-7Cd0I9Jp@google.com>
Date: Tue, 21 Oct 2025 11:27:39 -0700
From: Brian Norris <briannorris@...omium.org>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: "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 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.

Brian