Document dma_flags_set_attr(). Signed-off-by: Arthur Kepner <[EMAIL PROTECTED]>
--- DMA-API.txt | 27 +++++++++++++++++++++++++++ 1 files changed, 27 insertions(+) diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt index cc7a8c3..16e15c0 100644 --- a/Documentation/DMA-API.txt +++ b/Documentation/DMA-API.txt @@ -544,3 +544,30 @@ size is the size (and should be a page-sized multiple). The return value will be either a pointer to the processor virtual address of the memory, or an error (via PTR_ERR()) if any part of the region is occupied. + +int +dma_flags_set_attr(u32 attr, enum dma_data_direction dir) + +Amend dir with a platform-specific "dma attribute". + +The only attribute currently defined is DMA_BARRIER_ATTR, which causes +in-flight DMA to be flushed when the associated memory region is written +to (see example below). Setting DMA_BARRIER_ATTR provides a mechanism +to enforce ordering of DMA on platforms that permit DMA to be reordered +between device and host memory (within a NUMA interconnect). On other +platforms this is a nop. + +DMA_BARRIER_ATTR would be set when the memory region is mapped for DMA, +e.g.: + + int count; + int flags = dma_flags_set_attr(DMA_BARRIER_ATTR, DMA_BIDIRECTIONAL); + .... + count = dma_map_sg(dev, sglist, nents, flags); + +As an example of a situation where this would be useful, suppose that +the device does a DMA write to indicate that data is ready and +available in memory. The DMA of the "completion indication" could +race with data DMA. Using DMA_BARRIER_ATTR on the memory used for +completion indications would prevent the race. + - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
