Man page 9 : dma_pool_alloc

dma_pool_alloc - get a block of consistent memory

void * dma_pool_alloc(struct dma_pool *  pool , gfp_t  mem_flags , dma_addr_t *  handle );

pool
    dma pool that will produce the block

mem_flags
    GFP_* bitmask

handle
    pointer to dma address of block

This returns the kernel virtual address of a currently unused block, and reports its dma address through the handle. If such a memory block canAqt be allocated, NULL is returned.