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From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Matthew Garrett <mjg59@srcf.ucam.org>
Subject: Re: [RFD] Automatic suspend
Date: Fri, 27 Feb 2009 21:54:01 +0100
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Cc: Pavel Machek <pavel@ucw.cz>, "Arve Hj?nnev?g" <arve@android.com>,
       Alan Stern <stern@rowland.harvard.edu>,
       "Woodruff, Richard" <r-woodruff2@ti.com>,
       Arjan van de Ven <arjan@infradead.org>,
       Kyle Moffett <kyle@moffetthome.net>, Oliver Neukum <oliver@neukum.org>,
       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>,
       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>
References: <200902192215.18365.rjw@sisk.pl> <200902271522.41915.rjw@sisk.pl> <20090227142946.GA13650@srcf.ucam.org>
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On Friday 27 February 2009, Matthew Garrett wrote:
> On Fri, Feb 27, 2009 at 03:22:39PM +0100, Rafael J. Wysocki wrote:
> > On Friday 27 February 2009, Pavel Machek wrote:
> > > Wakelocks done right are single atomic_t... and if you set it to 0,
> > > you just unblock "sleeper" thread or something. Zero polling and very
> > > simple...
> > 
> > Except that you have to check all of the wakelocks periodically in a loop =>
> > polling.  So?
> 
> Why do you need to check them? If you're taking this approach you just 
> have something like:
> 
> suspend_unblock() {
> 	if (atomc_dec_and_test(&suspend_lock))
> 		suspend();
> }
> 
> and then check that the lock count is still 0 after device_suspend(). 
> There's no need to poll.

I was talking about wakelocks as originally proposed.

Using a refcount along with per-driver and per-process flags (probably two
refcounts would be more efficient in fact) is the latest idea and I agree it
wouldn't require polling.  However, if you refer to that, please don't use the
name "wakelock". :-)

Thanks,
Rafael