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

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Date:	Thu, 27 May 2010 20:58:21 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Paul@...p1.linux-foundation.org,
	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 Thu, 27 May 2010, Alan Cox wrote:

> > No, it's not. Forced suspend may be in response to hitting a key, but it 
> 
> You are the only person here talking about 'forced' suspends. The rest of
> us are talking about idling down and ensuring we are always in a state we
> un-idle correctly.
> 
> > may also be in response to a 30 minute timeout expiring. If I get a WoL 
> > packet in the 0.5 of a second between userspace deciding to suspend and 
> > actually doing so, the system shouldn't suspend.
> 
> I don't think that argument holds water in the form you have it
> 
> What about 5 nanoseconds before you suspend. Now you can't do that (laws
> of physics and stuff).
> 
> So your position would seem to be "we have a race but can debate how big
> is permissible"
> 
> The usual model is
> 
> "At no point should we be in a position when entering a suspend style
>  deep sleep where we neither abort the suspend, nor commit to a
>  suspend/resume sequence if the events we care about occur"
> 
> and that is why the hardware model is
> 
> 	Set wake flags
> 	Check if idle
> 	If idle
> 		Suspend
> 	else
> 		Clear wake flags
> 		Unwind
> 
> and the wake flags guarantee that an event at any point after the wake
> flags are set until they are cleared will cause a suspend to be resumed,
> possibly immediately after the suspend.

And if a platform can not guarantee the wakeup or the lossless
transition of states then you can not solve this by throwing blockers
or whatever into the code.

Thanks,

	tglx
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