// 用于一致性内存映射的映射范围
static inline int dma_set_coherent_mask(struct device *dev, u64 mask)
// 用于流式内存映射的映射范围
static inline int dma_set_mask(struct device *dev, u64 mask);

// dev        DMA控制器设备
// size        要分配的DMA buffer大小
// dma_handle  返回DMA buf的物理地址
// flag        分配标志
// 返回值       DMA buffer的虚拟地址
void *dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_handle, gfp_t flag) 

// dev        DMA控制器设备
// size        释放的DMA buffer大小
// cpu_addr    DMA buf的虚拟地址
// dma_handle  DMA buf的物理地址
void dma_free_coherent(struct device *dev, size_t size,
    void *cpu_addr, dma_addr_t dma_handle)

/**
 * dma_pool_alloc - 从dma poll获得一块一致性内存
 * @pool: 产生内存块的dma pool
 * @mem_flags: GFP_* bitmask
 * @handle: 返回内存块的dma地址
 */
void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
       dma_addr_t *handle)

/**
 * dma_pool_free - 将内存释放回dma pool
 * @pool:产生内存块的dma pool
 * @vaddr: 内存块的虚拟地址
 * @dma: 内存块的物理地址
 */
void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma)

// dev    需要映射内存的设备
// ptr     映射的buffer虚拟地址
// size    映射的大小
// dir     传输方向
// attr    属性
// 返回值   dma物理地址
dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr,
             size_t size,
             enum dma_data_direction dir,
             unsigned long attrs)
// dev    需要映射内存的设备
// addr   dma区域的物理地址
// size    映射的大小
// dir     传输方向
// attr    属性
void dma_unmap_single_attrs(struct device *dev, dma_addr_t addr,
           size_t size,
           enum dma_data_direction dir,
           unsigned long attrs)

dma_addr_t dma_map_page(struct device *dev, struct page *page,
           size_t offset, size_t size,
           enum dma_data_direction dir)

void dma_unmap_page(struct device *dev, dma_addr_t addr,
         size_t size, enum dma_data_direction dir)

// 返回dma映射错误
int dma_mapping_error(struct device *dev, dma_addr_t dma_addr)

int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
          int nents, enum dma_data_direction dir,
          unsigned long attrs)

void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
           int nents, enum dma_data_direction dir,
           unsigned long attrs)

// 返回map后的dma地址和长度
sg_dma_address(struct scatterlist *sg)
sg_dma_len(struct scatterlist *sg)

void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,
size_t size,
enum dma_data_direction dir)

void dma_sync_single_for_device(struct device *dev,
dma_addr_t addr, size_t size,
enum dma_data_direction dir)

void
dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
int nelems, enum dma_data_direction dir)

void
dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
int nelems, enum dma_data_direction dir)