2010-02-12 05:56:07 +08:00
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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 <mach/motherboard.h>
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#include "core.h"
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2011-01-19 18:24:56 +08:00
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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 18:53:12 +08:00
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2010-02-12 05:56:07 +08:00
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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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2011-03-01 00:01:04 +08:00
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ct_desc->init_cpu_map();
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2010-02-12 05:56:07 +08:00
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}
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2010-12-03 19:09:48 +08:00
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void __init platform_smp_prepare_cpus(unsigned int max_cpus)
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2010-02-12 05:56:07 +08:00
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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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2011-03-01 00:01:04 +08:00
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ct_desc->smp_enable(max_cpus);
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2010-12-03 19:09:48 +08:00
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2010-02-12 05:56:07 +08:00
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/*
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2010-12-03 19:09:48 +08:00
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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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2010-02-12 05:56:07 +08:00
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*/
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2012-01-25 23:37:29 +08:00
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v2m_flags_set(virt_to_phys(versatile_secondary_startup));
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2010-02-12 05:56:07 +08:00
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}
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