2010-02-11 21:56:07 +00:00
										 
									 
								 
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								/*
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								 *  linux/arch/arm/mach-vexpress/platsmp.c
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								 *
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								 *  Copyright (C) 2002 ARM Ltd.
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								 *  All Rights Reserved
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								 *
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								 * This program is free software; you can redistribute it and/or modify
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								 * it under the terms of the GNU General Public License version 2 as
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								 * published by the Free Software Foundation.
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								 */
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								#include <linux/init.h>
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								#include <linux/errno.h>
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								#include <linux/smp.h>
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								#include <linux/io.h>
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								#include <asm/unified.h>
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								#include <mach/motherboard.h>
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								#define V2M_PA_CS7 0x10000000
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								#include "core.h"
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											2011-01-19 10:24:56 +00:00
										 
									 
								 
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								extern void versatile_secondary_startup(void);
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												ARM: Fix subtle race in CPU pen_release hotplug code
There is a subtle race in the CPU hotplug code, where a CPU which has
been offlined can online itself before being requested, which results
in things going astray on the next online/offline cycle.
What happens in the normal online/offline/online cycle is:
	CPU0			CPU3
	requests boot of CPU3
	pen_release = 3
	flush cache line
				checks pen_release, reads 3
				starts boot
				pen_release = -1
	... requests CPU3 offline ...
				... dies ...
				checks pen_release, reads -1
	requests boot of CPU3
	pen_release = 3
	flush cache line
				checks pen_release, reads 3
				starts boot
				pen_release = -1
However, as the write of -1 of pen_release is not fully flushed back to
memory, and the checking of pen_release is done with caches disabled,
this allows CPU3 the opportunity to read the old value of pen_release:
	CPU0			CPU3
	requests boot of CPU3
	pen_release = 3
	flush cache line
				checks pen_release, reads 3
				starts boot
				pen_release = -1
	... requests CPU3 offline ...
				... dies ...
				checks pen_release, reads 3
				starts boot
				pen_release = -1
	requests boot of CPU3
	pen_release = 3
	flush cache line
Fix this by grouping the write of pen_release along with its cache line
flushing code to ensure that any update to pen_release is always pushed
out to physical memory.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
											
										 
										
											2010-12-18 10:53:12 +00:00
										 
									 
								 
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											2010-02-11 21:56:07 +00:00
										 
									 
								 
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								/*
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								 * Initialise the CPU possible map early - this describes the CPUs
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								 * which may be present or become present in the system.
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								 */
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								void __init smp_init_cpus(void)
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								{
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											2011-02-28 17:01:04 +01:00
										 
									 
								 
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									ct_desc->init_cpu_map();
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								}
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											2010-12-03 11:09:48 +00:00
										 
									 
								 
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								void __init platform_smp_prepare_cpus(unsigned int max_cpus)
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								{
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									/*
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									 * Initialise the present map, which describes the set of CPUs
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									 * actually populated at the present time.
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									 */
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											2011-02-28 17:01:04 +01:00
										 
									 
								 
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									ct_desc->smp_enable(max_cpus);
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											2010-02-11 21:56:07 +00:00
										 
									 
								 
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									/*
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											2010-12-03 11:09:48 +00:00
										 
									 
								 
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									 * Write the address of secondary startup into the
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									 * system-wide flags register. The boot monitor waits
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									 * until it receives a soft interrupt, and then the
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									 * secondary CPU branches to this address.
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											2010-02-11 21:56:07 +00:00
										 
									 
								 
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									 */
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											2010-12-03 11:09:48 +00:00
										 
									 
								 
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									writel(~0, MMIO_P2V(V2M_SYS_FLAGSCLR));
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											2011-01-19 10:24:56 +00:00
										 
									 
								 
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									writel(BSYM(virt_to_phys(versatile_secondary_startup)),
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										MMIO_P2V(V2M_SYS_FLAGSSET));
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								}
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