-
由 Marek Szyprowski 提交于
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! Signed-off-by: NMarek Szyprowski <m.szyprowski@samsung.com> Reviewed-by: NKyungmin Park <kyungmin.park@samsung.com>
bdf5e487