summaryrefslogtreecommitdiffstats
path: root/Documentation/DMA-API-HOWTO.txt
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/DMA-API-HOWTO.txt')
-rw-r--r--Documentation/DMA-API-HOWTO.txt16
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