linux-kernel - Re: [RFD] Automatic suspend

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Date:	Tue, 17 Feb 2009 00:02:36 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	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, Alan Stern wrote:
> On Mon, 16 Feb 2009, Rafael J. Wysocki wrote:
> 
> > 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)
> 
> Set the automatic PM parameters (idle timeout, state to go to, etc.).  

Yes.  I'm not sure about the state part, though.

> And disabling automatic PM altogether (effectively the same as setting
> the idle timeout to infinity).

Yes.

> > * check what power states devices are in.
> 
> What about situations where we want to distinguish between the power 
> state of the device itself and the power state of the link?  For a disk 
> drive we may want to power the link on and off quite a lot, as that 
> has low latency, but spinning the disk up and down takes a long time 
> and so should have a longer idle-time value.

Well, I'm not sure at the moment.

Do you have any suggestions?

Rafael
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