• Marek Szyprowski's avatar
    common: DMA-mapping: add DMA_ATTR_SKIP_CPU_SYNC attribute · bdf5e487
    Marek Szyprowski authored
    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: default avatarMarek Szyprowski <m.szyprowski@samsung.com>
    Reviewed-by: default avatarKyungmin Park <kyungmin.park@samsung.com>
    bdf5e487
dma-attrs.h 1.82 KB