Document dma_flags_set_dmabarrier(). Signed-off-by: Arthur Kepner <[EMAIL PROTECTED]>
--- DMA-API.txt | 26 ++++++++++++++++++++++++++ 1 files changed, 26 insertions(+) diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt index cc7a8c3..5fc0bba 100644 --- a/Documentation/DMA-API.txt +++ b/Documentation/DMA-API.txt @@ -544,3 +544,29 @@ 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_dmabarrier(int dir) + +Amend dir (one of the enum dma_data_direction values), with a +platform-specific "dmabarrier" attribute. The dmabarrier attribute +forces a flush of all in-flight DMA when the associated memory +region is written to (see example below.) + +This 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. + +The dmabarrier would be set when the memory region is mapped for DMA, +e.g.: + + int count, flags = dma_flags_set_dmabarrier(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 a dmabarrier 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/
