From 70ed0e02997b8a80dfd4f53af0e16fdf9ecdf6d0 Mon Sep 17 00:00:00 2001 From: Marek Szyprowski Date: Wed, 6 Jun 2012 14:46:44 +0200 Subject: [PATCH] common: DMA-mapping: add DMA_ATTR_SKIP_CPU_SYNC attribute This patch adds DMA_ATTR_SKIP_CPU_SYNC attribute to the DMA-mapping subsystem. By default dma_map_{single,page,sg} functions family transfer a given buffer from CPU domain to device domain. Some advanced use cases might require sharing a buffer between more than one device. This requires having a mapping created separately for each device and is usually performed by calling dma_map_{single,page,sg} function more than once for the given buffer with device pointer to each device taking part in the buffer sharing. The first call transfers a buffer from 'CPU' domain to 'device' domain, what synchronizes CPU caches for the given region (usually it means that the cache has been flushed or invalidated depending on the dma direction). However, next calls to dma_map_{single,page,sg}() for other devices will perform exactly the same sychronization operation on the CPU cache. CPU cache sychronization might be a time consuming operation, especially if the buffers are large, so it is highly recommended to avoid it if possible. DMA_ATTR_SKIP_CPU_SYNC allows platform code to skip synchronization of the CPU cache for the given buffer assuming that it has been already transferred to 'device' domain. This attribute can be also used for dma_unmap_{single,page,sg} functions family to force buffer to stay in device domain after releasing a mapping for it. Use this attribute with care! Change-Id: Idac6a165aacb0225aee6aa4c19cd6fb0df6772d5 Signed-off-by: Marek Szyprowski Reviewed-by: Kyungmin Park Git-commit: bdf5e4871f1b41150236e2337837399109469e65 Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git Signed-off-by: Laura Abbott --- Documentation/DMA-attributes.txt | 25 +++++++++++++++++++++++++ include/linux/dma-attrs.h | 1 + 2 files changed, 26 insertions(+) diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt index d62d0c6a236..019b476f56c 100644 --- a/Documentation/DMA-attributes.txt +++ b/Documentation/DMA-attributes.txt @@ -76,3 +76,28 @@ of mapping (no unaligned accesses, no re-ordering, no write merging, no buffering, no pre-fetching). This has severe performance penalties and should not be used for general purpose DMA allocations. It should only be used if one of the restrictions on strongly ordered memory is required. + +DMA_ATTR_SKIP_CPU_SYNC +---------------------- + +By default dma_map_{single,page,sg} functions family transfer a given +buffer from CPU domain to device domain. Some advanced use cases might +require sharing a buffer between more than one device. This requires +having a mapping created separately for each device and is usually +performed by calling dma_map_{single,page,sg} function more than once +for the given buffer with device pointer to each device taking part in +the buffer sharing. The first call transfers a buffer from 'CPU' domain +to 'device' domain, what synchronizes CPU caches for the given region +(usually it means that the cache has been flushed or invalidated +depending on the dma direction). However, next calls to +dma_map_{single,page,sg}() for other devices will perform exactly the +same sychronization operation on the CPU cache. CPU cache sychronization +might be a time consuming operation, especially if the buffers are +large, so it is highly recommended to avoid it if possible. +DMA_ATTR_SKIP_CPU_SYNC allows platform code to skip synchronization of +the CPU cache for the given buffer assuming that it has been already +transferred to 'device' domain. This attribute can be also used for +dma_unmap_{single,page,sg} functions family to force buffer to stay in +device domain after releasing a mapping for it. Use this attribute with +care! + diff --git a/include/linux/dma-attrs.h b/include/linux/dma-attrs.h index 74f6714663e..6c847e63721 100644 --- a/include/linux/dma-attrs.h +++ b/include/linux/dma-attrs.h @@ -18,6 +18,7 @@ enum dma_attr { DMA_ATTR_NO_KERNEL_MAPPING, DMA_ATTR_STRONGLY_ORDERED, DMA_ATTR_SKIP_ZEROING, + DMA_ATTR_SKIP_CPU_SYNC, DMA_ATTR_MAX, };