Detailed explanation of Linux DMA interface knowledge points

1. Two types of DMA mapping

1.1. Consistent DMA mappings

Mainly used to map areas that are used for long periods of time.

The CPU and DMA controller do not need to consider the impact of cache.

The consistency here is actually the concept of coherent, which cannot be guaranteed. In other words, a memory barrier is needed to ensure memory order.

1.2 Streaming DMA mapping

It is mainly used for one-time DMA transfer and will be released after the transfer is completed.

2. Specify the addressing range of the DMA device

include/linux/dma-mapping.h

// Mapping range for consistent memory mapping static inline int dma_set_coherent_mask(struct device *dev, u64 mask)
// Mapping range for streaming memory mapping static inline int dma_set_mask(struct device *dev, u64 mask);

3.DMA mapping interface

3.1 Coherent DMA Interface

Allocate a larger DMA buffer

// dev DMA controller device // size DMA buffer size to be allocated // dma_handle returns the physical address of DMA buf // flag allocation flag // return value virtual address of DMA buffer void *dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_handle, gfp_t flag) 

// dev DMA controller device // size size of the released DMA buffer // cpu_addr virtual address of DMA buf // dma_handle physical address of DMA buf void dma_free_coherent(struct device *dev, size_t size,
    void *cpu_addr, dma_addr_t dma_handle)

Allocate a smaller DMA buffer and apply for it from dma poll.

/**
 * dma_pool_alloc - get a block of consistent memory from dma poll * @pool: dma pool that generates memory blocks
 * @mem_flags: GFP_* bitmask
 * @handle: return the dma address of the memory block */
void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
       dma_addr_t *handle)

/**
 * dma_pool_free - release memory back to dma pool
 * @pool: dma pool that generates memory blocks
 * @vaddr: virtual address of memory block* @dma: physical address of memory block*/
void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma)

3.2 Streaming DMA Interface

// dev device that needs to map memory // ptr mapped buffer virtual address // size mapped size // dir transfer direction // attr attribute // return value dma physical address dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr,
             size_t size,
             enum dma_data_direction dir,
             unsigned long attrs)
// dev device that needs to map memory // addr physical address of dma area // size size of mapping // dir transfer direction // attr attribute void dma_unmap_single_attrs(struct device *dev, dma_addr_t addr,
           size_t size,
           enum dma_data_direction dir,
           unsigned long attrs)

Page Mapping

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)

Returns dma mapping error

// Return dma mapping error int dma_mapping_error(struct device *dev, dma_addr_t dma_addr)

Mapping scatterlist

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)

// Return the dma address and length after map sg_dma_address(struct scatterlist *sg)
sg_dma_len(struct scatterlist *sg)

Sync Operation

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)

The above are all the relevant knowledge points introduced this time. If you have any additions, please contact the editor of 123WORDPRESS.COM.

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