linux-kernel - Re: [RFD] Automatic suspend

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Message-ID: <20090302143422.GE2527@elf.ucw.cz>
Date:	Mon, 2 Mar 2009 15:34:22 +0100
From:	Pavel Machek <pavel@....cz>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	Arve Hj?nnev?g <arve@...roid.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	"Woodruff, Richard" <r-woodruff2@...com>,
	Arjan van de Ven <arjan@...radead.org>,
	Kyle Moffett <kyle@...fetthome.net>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	mark gross <mgross@...ux.intel.com>,
	Uli Luckas <u.luckas@...d.de>,
	Igor Stoppa <igor.stoppa@...ia.com>,
	Brian Swetland <swetland@...gle.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFD] Automatic suspend

On Mon 2009-03-02 09:24:36, Oliver Neukum wrote:
> Am Sonntag 01 März 2009 23:56:47 schrieb Pavel Machek:
> > > Allowing user space to suspend input devices while they are still open
> > > is useful. The user-space code that reads from the input devices does
> > > not need to know if the device is suspended or not, and the kernel
> > > cannot auto suspend input devices based on inactivity.
> >
> > Actually, I'd like you to fix your userspace and close input devices
> > when it does not need them. Given the way you control the platform it
> > should not be that hard. I do not see why we'd want to invent new
> > interface for "uhuh, I have opened the keyboard but I am not really
> > interested in keys being pressed".
> 
> Generally you can't do this. A task has an open fd.
> 
> - you cannot assume it can open the device again (fd may be
> inherited)

Well, those tasks that matter - X servers and similar - usually can.

> - keeping the device open makes sure you are talking to the same device

Well, you have to handle hotplug anyway, so... and the name will not
change unless you unplug/replug.

> - you may want to avoid repeating expensive initialisations

That kind of initializations should perhaps be done at insmod, not
open time?

> - some input devices also do output

I guess you want to separate those to two different devices, then.

Anyway...

* I'd prefer "close to powersave". I can see that can be tricky to
use. So the alternative is

* ioctl() "I'm not interested in exact keys, powersave" is something
that makes sense. It should really be discussed with input people.

I'd hate to see

* magic /sys/.../file where you echo 1 to powersave. It is too
disconnected from the input fd, and while it may make it easier to
retrofit powermanagement without modifying Xservers etc... it will
ultimately result in pretty ugly hacks.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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