DESC_INDEX
#define DMA_RINGS_SIZE (DMA_RING_SIZE * (DESC_INDEX + 1))
if (seq == 0 && DESC_INDEX(desc_ring, id) != 0)
info->seq = DESC_INDEX(desc_ring, id);
return &desc_ring->descs[DESC_INDEX(desc_ring, n)];
return &desc_ring->infos[DESC_INDEX(desc_ring, n)];