linux-kernel - Re: [RFC][PATCH] PM: Make PM core handle device registrations concurrent with suspend/hibernation

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Date:	Thu, 6 Mar 2008 12:40:37 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	Pavel Machek <pavel@....cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] PM: Make PM core handle device registrations
 concurrent with suspend/hibernation

On Thu, 6 Mar 2008, Rafael J. Wysocki wrote:

> > I thought of one more thing you might want to add: device_pm_add() 
> > doesn't handle the case where dev->parent is NULL.
> 
> I'm not sure what you mean.
> 
> If dev->parent is NULL, we get into the "successful" branch where the device is
> added to dpm_active.  Do you think we should add any extra handling of this
> case?

If a device is registered after dpm_suspend() has returned, the
device won't be suspended properly before the system goes to sleep.  

If the device has a parent then you're okay, because the parent must
already be suspended and so device_pm_add() will fail.  But if the
device doesn't have a parent then device_pm_add() will succeed, which
you don't want.

> > You could put in that static "all_devices_sleeping" flag, which gets set at
> > the end of dpm_suspend() and cleared at the start of dpm_resume().
> 
> Well, I don't think it's necessary.  dpm_active is empty in that case and
> we can use the list_empty(&dpm_active) check instead.

What would happen the very first time the system registers a device 
during startup?

Alan Stern

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