linux-kernel - Re: [RFD] Automatic suspend

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Message-ID: <Pine.LNX.4.44L0.0902270943490.2926-100000@iolanthe.rowland.org>
Date:	Fri, 27 Feb 2009 09:46:16 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Pavel Machek <pavel@....cz>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Oliver Neukum <oliver@...kum.org>,
	Arve Hj?nnev?g <arve@...roid.com>,
	"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 Fri, 27 Feb 2009, Pavel Machek wrote:

> 
> > To summarize, we can:
> > * Use a refcount such that automatic suspend will only be possible if it's
> >   equal to zero (but that need not be the only criterion).
> > * Use a per-device flag in dev_pm_info that will be set whenever the device
> >   driver increases the refcount and unset whenever the driver decreases the
> >   refcount.
> > * Use a per-process flag that will be set whenever the process increases the
> >   refcount and unset whenever the process decreases the refcount.
> 
> Yes, that sounds sane, and that's how reasonable wakelock
> implementation should look like.

One small point: If you add a per-device flag and a per-process flag as 
described above, then drivers and processes must not acquire nested 
references.

Obviously this is fixable, but it's worth mentioning...

Alan Stern

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