linux-kernel - Re: [RFD] Automatic suspend

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Message-Id: <200903020924.42451.oliver@neukum.org>
Date:	Mon, 2 Mar 2009 09:24:36 +0100
From:	Oliver Neukum <oliver@...kum.org>
To:	Pavel Machek <pavel@....cz>
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

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)
- keeping the device open makes sure you are talking to the same device
- you may want to avoid repeating expensive initialisations
- some input devices also do output

	Regards
		Oliver

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