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From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Alan Stern <stern@rowland.harvard.edu>
Subject: Re: [RFD] Automatic suspend
Date: Fri, 27 Feb 2009 21:58:29 +0100
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Cc: Pavel Machek <pavel@ucw.cz>, Oliver Neukum <oliver@neukum.org>,
       "Arve Hj?nnev?g" <arve@android.com>,
       "Woodruff, Richard" <r-woodruff2@ti.com>,
       Arjan van de Ven <arjan@infradead.org>,
       Kyle Moffett <kyle@moffetthome.net>,
       Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       pm list <linux-pm@lists.linux-foundation.org>,
       LKML <linux-kernel@vger.kernel.org>,
       Nigel Cunningham <nigel@nigel.suspend2.net>,
       Matthew Garrett <mjg59@srcf.ucam.org>,
       mark gross <mgross@linux.intel.com>, Uli Luckas <u.luckas@road.de>,
       Igor Stoppa <igor.stoppa@nokia.com>,
       Brian Swetland <swetland@google.com>, Len Brown <lenb@kernel.org>
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On Friday 27 February 2009, Alan Stern wrote:
> 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...

Yes, it's important to remeber IMO.

Thanks,
Rafael