From e7c5650f6067f65f8e961394f376d4862808d0d2 Mon Sep 17 00:00:00 2001 From: Catalin Marinas Date: Wed, 24 Mar 2010 16:49:54 +0100 Subject: ARM: 5996/1: ARM: Change the mandatory barriers implementation (4/4) The mandatory barriers (mb, rmb, wmb) are used even on uniprocessor systems for things like ordering Normal Non-cacheable memory accesses with DMA transfer (via Device memory writes). The current implementation uses dmb() for mb() and friends but this is not sufficient. The DMB only ensures the relative ordering of the observability of accesses by other processors or devices acting as masters. In case of DMA transfers started by writes to device memory, the relative ordering is not ensured because accesses to slave ports of a device are not considered observable by the DMB definition. A DSB is required for the data to reach the main memory (even if mapped as Normal Non-cacheable) before the device receives the notification to begin the transfer. Furthermore, some L2 cache controllers (like L2x0 or PL310) buffer stores to Normal Non-cacheable memory and this would need to be drained with the outer_sync() function call. The patch also allows platforms to define their own mandatory barriers implementation by selecting CONFIG_ARCH_HAS_BARRIERS and providing a mach/barriers.h file. Note that the SMP barriers are unchanged (being DMBs as before) since they are only guaranteed to work with Normal Cacheable memory. Signed-off-by: Catalin Marinas Signed-off-by: Russell King --- arch/arm/mm/Kconfig | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'arch/arm/mm/Kconfig') diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig index 55a2a00db77f..5bd7c89a6045 100644 --- a/arch/arm/mm/Kconfig +++ b/arch/arm/mm/Kconfig @@ -788,3 +788,9 @@ config ARM_L1_CACHE_SHIFT int default 6 if ARM_L1_CACHE_SHIFT_6 default 5 + +config ARCH_HAS_BARRIERS + bool + help + This option allows the use of custom mandatory barriers + included via the mach/barriers.h file. -- cgit v1.2.2