linux-kernel - Re: [linux-pm] Fundamental flaw in system suspend, exposed by freezer removal

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Date:	Tue, 4 Mar 2008 00:18:36 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Alexey Starikovskiy <astarikovskiy@...e.de>
Subject: Re: [linux-pm] Fundamental flaw in system suspend, exposed by freezer removal

On Tuesday, 4 of March 2008, Alan Stern wrote:
> On Mon, 3 Mar 2008, Rafael J. Wysocki wrote:
> 
> > > > Perhaps it's better to include dpm_sysfs_add() into device_pm_add(), since we
> > > > are going the make the return a result anyway?
> > > 
> > > Yes.
> > 
> > Okay, I'll prepare a patch for that, on top of the one introducing the
> > 'sleeping' field into 'struct dev_pm_info' (posting in a while).
> 
> While you're at it, could you add a field to indicate whether 
> begin_sleep() has been called?  It would help prevent multiple calls to 
> that method when a race does occur, and it could be useful for drivers 
> as well.

That will be added along with the new callbacks.

I'd prefer to do all that in separate patches, so that it's clear what issue is
addressed and how, by each of them.

> > The question remains what we're going to do with the drivers without pm_ops
> > pointers in the long run (in the short run we will use the legacy callbacks in
> > that cases, if defined).
> 
> One possibility is to unbind those drivers at the start of a sleep
> transition and reprobe them at the end.

That sounds promising.

> Another possibility is to ignore the lack of PM support and hope it doesn't
> cause any problems. 

That would be easy, but that's what we do now and there are problems with it.

Thanks,
Rafael
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