linux-kernel - Re: [RFD] Automatic suspend

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Date:	Fri, 20 Feb 2009 21:56:11 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Kyle Moffett <kyle@...fetthome.net>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	Alan Stern <stern@...land.harvard.edu>,
	"Woodruff, Richard" <r-woodruff2@...com>,
	Arjan van de Ven <arjan@...radead.org>,
	Oliver Neukum <oliver@...kum.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@....cz>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	mark gross <mgross@...ux.intel.com>,
	Uli Luckas <u.luckas@...d.de>,
	Igor Stoppa <igor.stoppa@...ia.com>,
	Brian Swetland <swetland@...gle.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFD] Automatic suspend

On Friday 20 February 2009, Kyle Moffett wrote:
> On Fri, Feb 20, 2009 at 10:56 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > * Introduce /sys/power/sleep that will work like /sys/power/state, but:
> >  - First, it will call ->acknowledge() for each driver (via bus types) to
> >    check if any of them wants to postpone the suspend (this will prevent tasks
> >    from being frozen unnecessarily if it is known in advance that the suspend
> >    should not happen at the moment).
> >  - Next, it will check the "I_do_not_want_automatic_suspend_to_occur" flag
> >    of each process and the suspend will be aborted if it is true for any of
> >    them (quite frankly, I think that should be integrated with the freezer,
> >    in particular the tasks that have TIF_FREEZE set shouldn't be able to set
> >    this flag and it should be checked in the freezer loop for every task with
> >    TIF_FREEZE unset).
> >  - Next, it will proceed with suspending just like /sys/power/state does (the
> >    drivers that missed the opportunity to abort the suspend by returning
> >    'false' from ->acknowledge() can still abort the suspend by failing their
> >    ->suspend() routines).
> >
> > Then, the decision making logic will be able to use /sys/power/sleep whenever
> > it wishes to and the kernel will be able to refuse to suspend if it's not
> > desirable at the moment.
> 
> Then, for a userspace process handling input events:
> 
> 1)  Unset "no-suspend flag"
> 2)  Poll event device
> 3)  When the poll returns true, set the "no-suspend flag"
> 4)  Read the event device and process the event(s)
> 5)  Go back to step 1
> 
> The event driver would responsible for atomically preventing suspend
> from the moment a button is pressed until it is actually delivered to
> a userspace process.  Since at that time the userspace process will be
> preventing suspend, there will be no window in which we could go to
> sleep with pending events.

That's correct.

How would you like to prevent it from happening?

Rafael
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