linux-kernel - Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

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Date:	Thu, 27 May 2010 20:59:24 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Florian Mickler <florian@...kler.org>,
	<felipe.balbi@...ia.com>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

On Fri, 28 May 2010, Rafael J. Wysocki wrote:

> > And the forced-suspend design relies on the fact that processes remain 
> > frozen throughout.  If we leave some processes unfrozen and one of them 
> > somehow becomes runnable, that means we have to abort the forced 
> > suspend before the process is allowed to run.
> 
> We could avoid that if drivers could block tasks, but there are questions to
> answer.  First off, how a driver is supposed to know when to block the task
> using it and when to do its power management transparently for the task?
> Second, how to intercept and block all possible interfaces that user space
> can use to talk to drivers (how to intercept a task using mmapped device, for
> example)?

We talked about this a few years ago and decided it was not feasible.  
It would require substantial changes to every device driver.

Alan Stern

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