ARM: Optionally allow ARMv6 to use 'normal, bufferable' memory for DMA

[safe/jmp/linux-2.6] / arch / arm / mm / Kconfig

diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index c4ed9f9..573528d 100644 (file)
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -781,3 +781,22 @@ config ARM_L1_CACHE_SHIFT
        int
        default 6 if ARM_L1_CACHE_SHIFT_6
        default 5
+
+config ARM_DMA_MEM_BUFFERABLE
+       bool "Use non-cacheable memory for DMA" if CPU_V6 && !CPU_V7
+       default y if CPU_V6 || CPU_V7
+       help
+         Historically, the kernel has used strongly ordered mappings to
+         provide DMA coherent memory.  With the advent of ARMv7, mapping
+         memory with differing types results in unpredictable behaviour,
+         so on these CPUs, this option is forced on.
+
+         Multiple mappings with differing attributes is also unpredictable
+         on ARMv6 CPUs, but since they do not have aggressive speculative
+         prefetch, no harm appears to occur.
+
+         However, drivers may be missing the necessary barriers for ARMv6,
+         and therefore turning this on may result in unpredictable driver
+         behaviour.  Therefore, we offer this as an option.
+
+         You are recommended say 'Y' here and debug any affected drivers.