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Diffstat (limited to 'Documentation/DMA-API-HOWTO.txt')
| -rw-r--r-- | Documentation/DMA-API-HOWTO.txt | 16 |
1 files changed, 13 insertions, 3 deletions
diff --git a/Documentation/DMA-API-HOWTO.txt b/Documentation/DMA-API-HOWTO.txt index 98ce51796f71..d568bc235bc0 100644 --- a/Documentation/DMA-API-HOWTO.txt +++ b/Documentation/DMA-API-HOWTO.txt @@ -738,21 +738,31 @@ to "Closing". CONFIG_NEED_SG_DMA_LENGTH if the architecture supports IOMMUs (including software IOMMU). -2) ARCH_KMALLOC_MINALIGN +2) ARCH_DMA_MINALIGN Architectures must ensure that kmalloc'ed buffer is DMA-safe. Drivers and subsystems depend on it. If an architecture isn't fully DMA-coherent (i.e. hardware doesn't ensure that data in the CPU cache is identical to data in main memory), - ARCH_KMALLOC_MINALIGN must be set so that the memory allocator + ARCH_DMA_MINALIGN must be set so that the memory allocator makes sure that kmalloc'ed buffer doesn't share a cache line with the others. See arch/arm/include/asm/cache.h as an example. - Note that ARCH_KMALLOC_MINALIGN is about DMA memory alignment + Note that ARCH_DMA_MINALIGN is about DMA memory alignment constraints. You don't need to worry about the architecture data alignment constraints (e.g. the alignment constraints about 64-bit objects). +3) Supporting multiple types of IOMMUs + + If your architecture needs to support multiple types of IOMMUs, you + can use include/linux/asm-generic/dma-mapping-common.h. It's a + library to support the DMA API with multiple types of IOMMUs. Lots + of architectures (x86, powerpc, sh, alpha, ia64, microblaze and + sparc) use it. Choose one to see how it can be used. If you need to + support multiple types of IOMMUs in a single system, the example of + x86 or powerpc helps. + Closing This document, and the API itself, would not be in its current |