linux-kernel - Re: [PATCH v4 4/5] msm: hotplug: support cpu hotplug on msm

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Message-ID: <20101214173007.GA24303@n2100.arm.linux.org.uk>
Date:	Tue, 14 Dec 2010 17:30:07 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Jeff Ohlstein <johlstei@...eaurora.org>
Cc:	David Brown <davidb@...eaurora.org>,
	Daniel Walker <dwalker@...eaurora.org>,
	linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Brian Swetland <swetland@...gle.com>,
	Dima Zavin <dima@...roid.com>,
	Arve Hj�nnev�g <arve@...roid.com>,
	Bryan Huntsman <bryanh@...eaurora.org>
Subject: Re: [PATCH v4 4/5] msm: hotplug: support cpu hotplug on msm

On Mon, Dec 13, 2010 at 08:50:32PM -0800, Jeff Ohlstein wrote:
> +static inline void platform_do_lowpower(unsigned int cpu)
> +{
> +	/* Just enter wfe for now. */
> +	for (;;) {
> +		asm("wfe" : : : "memory");
> +		if (pen_release == cpu) {
> +			/*
> +			 * OK, proper wakeup, we're done
> +			 */
> +			break;
> +		}
> +		smp_rmb();

I can't work out what this read memory barrier is doing here.  Could you
suggest what purpose it's serving please?
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