linux-kernel - Re: [linux-pm] suspend blockers & Android integration

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Date:	Thu, 10 Jun 2010 10:39:50 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	david@...g.hm
cc:	Arve Hjønnevåg <arve@...roid.com>,
	<tytso@....edu>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Florian Mickler <florian@...kler.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Brian Swetland <swetland@...gle.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>, Neil Brown <neilb@...e.de>,
	James Bottomley <James.Bottomley@...e.de>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Felipe Balbi <felipe.balbi@...ia.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [linux-pm] suspend blockers & Android integration

On Wed, 9 Jun 2010 david@...g.hm wrote:

> why could the suspend blocker process see all events, but the power 
> manager process not see the events?
> 
> have the userspace talk to the power manager the way it does to the 
> suspend blocker now and what's the difference?
> 
> effectivly think s/suspend blocker/power manager/ (with the power manager 
> doing all the other things that are proposed instead of grabbing the 
> wakelock), the difference should be hidden to the rest of userspace.
> 
> what am I missing here?

The main difference is that with a userspace power manager, programs
have to tell the power manager whenever they open or close a
wakeup-capable device file (and send it a copy of the file descriptor).  
With an in-kernel implementation these extra steps aren't needed,
because of course kernel drivers already know when their device files
are opened or closed.

Alan Stern

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