Message-Id: <201005280205.01561.rjw@sisk.pl>
Date:	Fri, 28 May 2010 02:05:01 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alan Stern <stern@...land.harvard.edu>,
	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>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Brian Swetland <swetland@...gle.com>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

On Friday 28 May 2010, Alan Cox wrote:
> > The approach with user space power manager suggested by Dmitry and Alan Stern
> > may work, but it still assumes some kind of suspend blockers to be present in
> > the kernel.  If we reject that too, I wonder what approach Google is supposed
> > to use and still get the same battery life they get with suspend blockers.
> 
> I'm getting less convinced it needs suspend blockers at all for this case,
> assuming that you are willing to have a policy that is based on
> 
> - assuming apps play nicely
> - having the information to user space you need (who woke us, who blocked
>   us, events)
> - dealing with offenders primarily from user space using that information
> 
> I'm fairly happy about the following so far
> 
> - we should have a common interface for seeing some pm events (like
>   duh ?) but it does need careful thought so the watcher doesn't change
>   the behaviour and break it. (Message "We are suspending", gosh someone
>   is running to receive the message, resume being the obvious case)
> 
> - Suspend is (for many platforms) just a cotinuation down the power
>   chain. Demonstrated and implemented on ARM. Very much the direction of
>   S0i1/S0i3 on x86 MID devices. Proved by the fact it has been done and
>   made to work, and by reading the Moorestown PR.
> 
> - Given a non forced (that is 'idle down') transition to a suspend level
>   we can implement a 'suspend as idle' on many embedded platforms in a
>   manner which is not racy at kernel level. Apparently implemented
>   already on ARM
> 
> - Given a non forced transition to such a suspend level and the reporting
>   of certain events we can do a full user space managed graphical UI type
>   environment policy in a race free fashion
> 
> - With notification of who caused a resume and maybe a bit of other
>   general stat gathering it is possible to identify and handle abuses of
>   power resource. Proved by the fact we can do this with powertop but
>   more elegance in the interfaces would be nice.
> 
> I am not sure if a pm event is what is needed for this or a sum 'hardware
> triggered wake up' event.
> 
> I accept that current ACPI based laptops probably couldn't make use of
> such a feature but I don't think this is important at the moment.

No, it's not.

> A resource constraint model might help further in the ACPI case. It's
> useful for other stuff but it might well be a distraction and
> implementation detail in terms of the basic question about what is needed
> for something like Android.
> 
> At this point the input of the Android team and the Nokia people would
> be rather more useful to me.

OK, I added Arve and Brian to the CC list.

Thanks,
Rafael
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