ARM: 6188/1: Add a config option for the ARM11MPCore DMA cache maintenance workaround
Commit f4d6477f introduced a workaround for the lack of hardware
broadcasting of the cache maintenance operations on ARM11MPCore.
However, the workaround is only valid on CPUs that do not do speculative
loads into the D-cache.
This patch adds a Kconfig option with the corresponding help to make the
above clear. When the DMA_CACHE_RWFO option is disabled, the kernel
behaviour is that prior to the f4d6477f commit. This also allows ARMv6
UP processors with speculative loads to work correctly.
For other processors, a different workaround may be needed.
Cc: Ronen Shitrit <rshitrit@marvell.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 346ae14..fc1b2fa 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -735,6 +735,25 @@
Forget about fast user space cmpxchg support.
It is just not possible.
+config DMA_CACHE_RWFO
+ bool "Enable read/write for ownership DMA cache maintenance"
+ depends on CPU_V6 && SMP
+ default y
+ help
+ The Snoop Control Unit on ARM11MPCore does not detect the
+ cache maintenance operations and the dma_{map,unmap}_area()
+ functions may leave stale cache entries on other CPUs. By
+ enabling this option, Read or Write For Ownership in the ARMv6
+ DMA cache maintenance functions is performed. These LDR/STR
+ instructions change the cache line state to shared or modified
+ so that the cache operation has the desired effect.
+
+ Note that the workaround is only valid on processors that do
+ not perform speculative loads into the D-cache. For such
+ processors, if cache maintenance operations are not broadcast
+ in hardware, other workarounds are needed (e.g. cache
+ maintenance broadcasting in software via FIQ).
+
config OUTER_CACHE
bool