dma_free_coherent
static void dma_free_coherent(struct device *, size_t, volatile void *, dma_addr_t);
dma_free_coherent(xmm->dev, sizeof(struct control_page), (volatile void *)xmm->cp, xmm->cp_phys);
dma_free_coherent(xmm->dev, ring->page_size, ring->pages[i], ring->pages_phys[i]);
dma_free_coherent(xmm->dev, sizeof(struct td_ring_entry)*depth, ring->tds, ring->tds_phys);