linux-kernel - Re: [PATCH] driver core: Ensure proper suspend/resume ordering

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Message-ID: <Pine.LNX.4.44L0.1509161259480.1993-100000@iolanthe.rowland.org>
Date:	Wed, 16 Sep 2015 13:08:03 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
cc:	Thierry Reding <thierry.reding@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	<linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] driver core: Ensure proper suspend/resume ordering

On Wed, 16 Sep 2015, Rafael J. Wysocki wrote:

> > The core prohibits new devices from being registered.  It does not 
> > prohibit probes of existing devices, because they currently do not 
> > affect the dpm_list.
> 
> Which may be a mistake, because it does affect callbacks executed during
> suspend/resume (after successful probe the device potentially has a different
> set of PM callbacks than before).
> 
> > In general, we rely on subsystems not to do any probing once a device 
> > is suspended.  It's probably reasonable to ask them not to do any 
> > probing once a device has gone through the "prepare" stage.
> 
> Right.
> 
> Question is when it should be allowed to probe again.  I guess at the same
> time we allow registrations to to take place again?

That would make the most sense.  Particularly since registration 
automatically causes probing to occur.

Now, we do allow registration below a device as soon as the ->resume
callback returns, whereas devices don't get added back to the dpm_list
until after the "complete" phase is totally finished.  If a
previously-existing device gets probed in between, it would be moved 
off the dpm_prepared_list before its ->complete callback was invoked, 
which means its ->complete wouldn't get called at all.

Perhaps this would be okay; it depends on the subsystem.

Alan Stern

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