linux-kernel - Re: [suspend/resume] Re: userspace notification from module

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Date:	Sat, 16 Jan 2010 23:19:30 +0100
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Stanislav Brabec <utx@...guin.cz>,
	Eric Miao <eric.y.miao@...il.com>,
	Bart?omiej Zimo? <uzi18@...pl>, Andy Walls <awalls@...ix.net>,
	Daniel Borkmann <danborkmann@...glemail.com>,
	linux-kernel@...r.kernel.org, rpurdie@...ys.net, lenz@...wisc.edu,
	Dirk@...er-online.de, arminlitzel@....de,
	Cyril Hrubis <metan@....cz>, thommycheck@...il.com,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	dbaryshkov@...il.com, omegamoon@...il.com,
	zaurus-devel@...ts.linuxtogo.org
Subject: Re: [suspend/resume] Re: userspace notification from module

On Sat 2010-01-16 23:05:56, Rafael J. Wysocki wrote:
> On Saturday 16 January 2010, Pavel Machek wrote:
> > On Sat 2010-01-16 18:00:58, Stanislav Brabec wrote:
> > > Eric Miao wrote:
> > > 
> > > > And the other way we may need to look into what API the current userland
> > > > apps on zaurus is depending on this 2.4 compatibility and make changes
> > > > slowly to those apps.
> > > 
> > > I guess that 2.4 compatibility is not an issue. Most modern Zaurus
> > > distributions are even unable to run Sharp ROM compatible binaries.
> > > 
> > > Distributions either stay on 2.4 kernel or use modern systems based on
> > > modern kernel 2.6 API.
> > > 
> > > Distributions that decided to migrate to kernel 2.6 are far from
> > > finished state. Any change that allows to use modern applications using
> > > standard kernel API is welcome.
> > 
> > There is no API involved. It is just ... if you leave zaurus in
> >  init=/bin/bash mode, it must not kill the battery. Smart and
> >  currently implemented way to do that is to suspend.
> 
> IMHO it should just plain shutdown in that case.  Suspending doesn't really
> solve the problem, because the battery is going to drain still.  Unless you
> mean suspend=hibernate, but I guess you don't.

As I explained before, power consumption on suspend and hibernate and
poweroff is equivalent on zaurus (7mA in all the cases -- sorry if I
said uA before). And because it has 1800mAh battery, it means that
even empty battery is going to last for a while. In practice, it works
very well.

(There are other reasons, having to do with internal li-ion resistances
in aged and cold batteries.)

> > That's counterexample to rjw, but it does not matter -- reasonable
> > userland should never ever hit that, in a same way PCs should not hit
> > emergency power cut...
> 
> I don't really understand what you mean.  The user space doesn't know the
> battery state if the kernel doesn't tell it, AFAICS, so how exactly can it
> predict the critical battery condition without the kernel notifying it?

That was not the point I was trying to discuss. Yes, we need
kernel<->user notification of battery critical. 

But on zaurus, correct action is to suspend (not hibernate and not
poweroff) when battery is no longer able to supply enough power to
keep system alive.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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