td_ring_entry
struct td_ring_entry *tds;
ring->tds = dma_alloc_coherent(xmm->dev, sizeof(struct td_ring_entry)*depth, &ring->tds_phys, GFP_KERNEL);
dma_free_coherent(xmm->dev, sizeof(struct td_ring_entry)*depth, ring->tds, ring->tds_phys);