ARM: NOMMU: Set ARM_DMA_MEM_BUFFERABLE for M-class cpus

Now, we have dedicated non-cacheable region for consistent DMA
operations. However, that region can still be marked as bufferable by
MPU, so it'd be safer to have barriers by default. M-class machines
that didn't need it until now also likely won't need it in the future,
therefore, we offer this as an option.

Tested-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Tested-by: Andras Szemzo <sza@esh.hu>
Tested-by: Alexandre TORGUE <alexandre.torgue@st.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index c6c4c9c8824b0f4b3c354538306d1c195ad7e90d..877a0e3fd17d30796b8ec353c434ea42983037c0 100644 (file)
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -1045,8 +1045,8 @@ config ARM_L1_CACHE_SHIFT
        default 5
 
 config ARM_DMA_MEM_BUFFERABLE
-       bool "Use non-cacheable memory for DMA" if (CPU_V6 || CPU_V6K) && !CPU_V7
-       default y if CPU_V6 || CPU_V6K || CPU_V7
+       bool "Use non-cacheable memory for DMA" if (CPU_V6 || CPU_V6K || CPU_V7M) && !CPU_V7
+       default y if CPU_V6 || CPU_V6K || CPU_V7 || CPU_V7M
        help
          Historically, the kernel has used strongly ordered mappings to
          provide DMA coherent memory.  With the advent of ARMv7, mapping
@@ -1061,6 +1061,10 @@ config ARM_DMA_MEM_BUFFERABLE
          and therefore turning this on may result in unpredictable driver
          behaviour.  Therefore, we offer this as an option.
 
+         On some of the beefier ARMv7-M machines (with DMA and write
+         buffers) you likely want this enabled, while those that
+         didn't need it until now also won't need it in the future.
+
          You are recommended say 'Y' here and debug any affected drivers.
 
 config ARM_HEAVY_MB