From 47ab0dee661dbd5aca67abe44a333e471134fbf9 Mon Sep 17 00:00:00 2001 From: Russell King Date: Sat, 15 May 2010 11:02:43 +0100 Subject: ARM: Optionally allow ARMv6 to use 'normal, bufferable' memory for DMA Provide a configuration option to allow the ARMv6 to use normal bufferable memory for coherent DMA. This option is forced to 'y' for ARMv7, and offered as a configuration option on ARMv6. Enabling this option requires drivers to have the necessary barriers to ensure that data in DMA coherent memory is visible prior to the DMA operation commencing. Reviewed-by: Catalin Marinas Signed-off-by: Russell King --- arch/arm/mm/Kconfig | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) (limited to 'arch/arm/mm/Kconfig') diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig index c4ed9f93f646..573528d9c6d8 100644 --- 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. -- cgit v1.2.3