linux-kernel - Re: [RFD] Automatic suspend

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Message-ID: <20090227142946.GA13650@srcf.ucam.org>
Date:	Fri, 27 Feb 2009 14:29:46 +0000
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Pavel Machek <pavel@....cz>, Arve Hj?nnev?g <arve@...roid.com>,
	Alan Stern <stern@...land.harvard.edu>,
	"Woodruff, Richard" <r-woodruff2@...com>,
	Arjan van de Ven <arjan@...radead.org>,
	Kyle Moffett <kyle@...fetthome.net>,
	Oliver Neukum <oliver@...kum.org>,
	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>,
	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, 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.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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