linux-kernel - Re: [RFC PATCH v2 1/3] PM / Core: suspend

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Message-ID: <20110426221054.GB29092@elf.ucw.cz>
Date:	Wed, 27 Apr 2011 00:10:54 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	MyungJoo Ham <myungjoo.ham@...sung.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	linux-pm@...ts.linux-foundation.org,
	Len Brown <len.brown@...el.com>,
	"Jean Delvare (PC drivers core)" <khali@...ux-fr.org>,
	"Ben Dooks (embedded platforms)" <ben-linux@...ff.org>,
	kyungmin.park@...sung.com, myungjoo.ham@...il.com,
	LKML <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>, rpurdie@...ys.net,
	lenz@...wisc.edu, arminlitzel@....de, Cyril Hrubis <metan@....cz>,
	thommycheck@...il.com,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	dbaryshkov@...il.com, omegamoon@...il.com, eric.y.miao@...il.com,
	utx@...guin.cz, zaurus-devel@...ts.linuxtogo.org,
	Marek Vasut <marek.vasut@...il.com>
Subject: Re: [RFC PATCH v2 1/3] PM / Core: suspend_again callback for
 device PM.

Hi!

> > > And that's exactly what should be done.  Have a user space process controlling
> > > that, because avoiding to thaw user space doesn't buy us almost
> > > anything.
> > 
> > That makes Zaurus implement different user-kernel interface than PC
> > class machine, because of hardware quirk.
> 
> Let me say that again: If Zaurus needs to resume everything except for
> user space periodically to monitor the battery charger, I'm not sure if our
> suspend interface is the right one for it in the first place.

Well, Zaurus does not need to resume everything. SPI+charger code is
enough, and that would be preffered. No need to touch disk etc.

> It seriously looks like a workaround for the lack of appropriately implemented
> runtime PM, just like the Android's opportunistic suspend.

No, not really. I'm running standard Debian; I do not want/need
anything like opportunistic suspend.

> > > Now, I know that it's probably easier to modify the kernel than to write
> > > a user space tool for that, test it and so on, but "easier" is not necessarily
> > > "better".
> > 
> > It is easier, allows us to keep same user-kernel interface on PC and
> > Zaurus, and is compatible with 2.6.38.
> > 
> > Heck, I'm used to typing "echo mem > /sys/power/state". I should not
> > have to learn different interface just because Zaurus does not have
> > proper hardware charger.
> 
> No, this interface should not be used on Zaurus at all.  It's not mean for
> that and while you can hack it to kind of work, it still is hacking rather
> than designing things.

Why not? I want the Zaurus to sleep. Why should I have to know how its
charging unit works? Why should I use different interface than on PC?
I want it to suspend, put it into backpack and move...

> > Bootloader takes care of battery in that case.
> 
> So the difference is that we let someone else worry.  Cool. :-)

Yes.

> > Ok, see the spitz_should_wakeup() function in arch/arm/mach-pxa/* and
> > should_wakeup() usage.
> 
> OK, I will.

Thanks.
									Pavel

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