linux-kernel - Re: [Xen-devel] Re: [linux-pm] [PATCH 0/2] Fix hangup after creating checkpoint on Xen.

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Date:	Thu, 10 Feb 2011 11:40:05 +0000
From:	Ian Campbell <ijc@...lion.org.uk>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Brendan Cully <brendan@...ubc.ca>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"linux-pm@...ts.linux-foundation.org" 
	<linux-pm@...ts.linux-foundation.org>,
	"SUZUKI, Kazuhiro" <kaz@...fujitsu.com>
Subject: Re: [Xen-devel] Re: [linux-pm] [PATCH 0/2] Fix hangup after
 creating checkpoint on Xen.

On Wed, 2011-02-09 at 23:42 +0000, Alan Stern wrote:
> In fact there already is a "fast suspend & resume" path in the PM core.  
> It's the freeze/thaw procedure used when starting to hibernate.  The
> documentation specifically says that drivers' freeze methods are
> supposed to quiesce their devices but not change power levels.  In
> addition, the thaw method is invoked as part of recovery from a failed
> hibernation attempt, so it already has the "cancel" semantics that xen 
> seems to want.

Sounds like that would work and I would much prefer to simply make
correct use of the core functionality.

So PMSG_FREEZE is balanced by either PMSG_RECOVER or PMSG_THAW depending
on whether the suspend was cancelled or not? So the sequence of events
is something like:
	dpm_suspend_start(PMSG_FREEZE);
         
		dpm_suspend_noirq(PMSG_FREEZE);
                         
			sysdev_suspend(PMSG_QUIESCE);
			cancelled = suspend_hypercall()
			sysdev_resume();
                 
		dpm_resume_noirq(cancelled ? PMSG_RECOVER : PMSG_THAW);
         
	dpm_resume_end(cancelled ? PMSG_RECOVER : PMSG_THAW);
?

(For comparison we currently have:
> > >         dpm_suspend_start(PMSG_SUSPEND);
> > >         
> > >                 dpm_suspend_noirq(PMSG_SUSPEND);
> > >                         
> > >                         sysdev_suspend(PMSG_SUSPEND);
> > >                         /* suspend hypercall */
> > >                         sysdev_resume();
> > >                 
> > >                 dpm_resume_noirq(PMSG_RESUME);
> > >         
> > >         dpm_resume_end(PMSG_RESUME);
)

Ian.
-- 
Ian Campbell
Current Noise: Neil Young - Angry World

If only one could get that wonderful feeling of accomplishment without
having to accomplish anything.

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