Linux Device Drivers Development

Single-buffer mapping

This is for occasional mapping. One can set up a single buffer with this:

dma_addr_t dma_map_single(struct device *dev, void *ptr, 
         size_t size, enum dma_data_direction direction); 

The direction should be DMA_TO_DEVICE, DMA_FROM_DEVICE, or DMA_BIDIRECTIONAL, as described in the preceding code. ptr is the kernel virtual address of the buffer, and dma_addr_t is the returned bus address for the device. Make sure to use the direction that really fits your needs, not just always DMA_BIDIRECTIONAL.

One should free the mapping with this:

void dma_unmap_single(struct device *dev, dma_addr_t dma_addr, 
              size_t size, enum dma_data_direction direction);