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ARM: 6784/1: errata: no automatic Store Buffer drain on Cortex-A9

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On revisions of the Cortex-A9 prior to r2p0, the Store Buffer does not
have any automatic draining mechanism and therefore a livelock may occur
if an external agent continuously polls a memory location waiting to
observe an update.

This workaround defines cpu_relax() as smp_mb(), preventing correctly
written polling loops from denying visibility of updates to memory.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Will Deacon
2011-03-04 12:38:54 +01:00
committed by Russell King
parent fcbdc5fe6e
commit 5dab26af1b
2 changed files with 12 additions and 1 deletions
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2
arch/arm/include/asm/processor.h
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@@ -95,7 +95,7 @@ extern void release_thread(struct task_struct *);
unsigned long get_wchan(struct task_struct *p);
#if __LINUX_ARM_ARCH__ == 6
#if __LINUX_ARM_ARCH__ == 6 || defined(CONFIG_ARM_ERRATA_754327)
#define cpu_relax() smp_mb()
#else
#define cpu_relax() barrier()