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Message-Id: <200902162312.50556.rjw@sisk.pl>
Date: Mon, 16 Feb 2009 23:12:48 +0100
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: Arjan van de Ven <arjan@...radead.org>
Cc: pm list <linux-pm@...ts.linux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
Arve Hjønnevåg <arve@...roid.com>,
Alan Stern <stern@...land.harvard.edu>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Pavel Machek <pavel@....cz>,
Nigel Cunningham <nigel@...el.suspend2.net>,
Matthew Garrett <mjg59@...f.ucam.org>,
mark gross <mgross@...ux.intel.com>,
"Woodruff, Richard" <r-woodruff2@...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 Monday 16 February 2009, Arjan van de Ven wrote:
> On Mon, 16 Feb 2009 22:48:32 +0100
> "Rafael J. Wysocki" <rjw@...k.pl> wrote:
>
> > > Userland should never ever control the state of a device like this
> > > directly. It should do so by a) closing the device and b) setting
> > > latency / functional requirements.
> >
> > The user, however, may want to forcibly put a device into a low power
> > state without stopping all of the applications that depend on it (eg.
> > have it open). Do you think that we shouldn't allow users to do such
> > things?
>
> I would think that that is a bad mistake to do. It basically breaks the
> contract that the kernel has with userspace....
OK, so I think there are two things that user space may be allowed to do as
far as putting devices into low power states is concerned:
* disable/enable the automatic power management of the device (provided that
the driver supports the automatic PM)
* check what power states devices are in.
Thanks,
Rafael
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