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

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Message-ID: <20110426220653.GA29092@elf.ucw.cz>
Date:	Wed, 27 Apr 2011 00:06:53 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Greg KH <gregkh@...e.de>, MyungJoo Ham <myungjoo.ham@...sung.com>,
	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>
Subject: Re: [RFC PATCH v2 1/3] PM / Core: suspend_again callback for
 device PM.

Hi!

> > It certainly looks a lot like s2ram to the user.
> > 
> > Now, your PC wakes up periodically in s2ram, too; but it is keyboard
> > controller that wakes up, not CPU, so you do not know.
> 
> I seriously doubt it's a keyboard controller in contemporary machines.

> Yes, there are parts of them that don't actually sleep, but that's not
> under OS control.

Ok, so it is called "embedded controller" these days. But you got the
idea.

> > On Zaurus, you do not know, either; nothing visible happens and
> > userspace is shielded from these details.
> 
> If you wake up device drivers, it _is_ visible.  Maybe not to user
> space, but that's a semantic difference.

Just to clarify; not _all_ device drivers need to be woken up. Just
SPI + charger code is enough... and I guess it would be prefered
because spinning up disk just to toggle charger would be nasty.

> > Should user really have to know if battery charger is implemented on
> > keyboard controller or on main cpu before he selects which interface
> > to use?
> 
> Please don't confuse user space with the user.  You can resume all the
> way to user space without turning the backlight on and the user will not
> notice, right?

The user has to type "echo mem > /sys/power/state" :-). And you better
turn him the backlight on, typing blind is bad.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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