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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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11
arch/arm/Kconfig
View File

@ -1213,6 +1213,17 @@ config ARM_ERRATA_754322
the new ASID. This workaround places two dsb instructions in the mm
switching code so that no page table walks can cross the ASID switch.
config ARM_ERRATA_754327
bool "ARM errata: no automatic Store Buffer drain"
depends on CPU_V7 && SMP
help
This option enables the workaround for the 754327 Cortex-A9 (prior to
r2p0) erratum. 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.
endmenu
source "arch/arm/common/Kconfig"

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()