ARM: 6784/1: errata: no automatic Store Buffer drain on Cortex-A9
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>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index ec0f658..d3f2de3 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1213,6 +1213,17 @@
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"