RING_BUFFER_SIZE
intf->rx_buf_order = get_order(RING_BUFFER_SIZE);
intf->rx_ring_dma = dma_map_page(kdev, buffer_pg, 0, RING_BUFFER_SIZE,
dma_unmap_page(kdev, intf->rx_ring_dma, RING_BUFFER_SIZE,
dma_unmap_page(kdev, intf->rx_ring_dma, RING_BUFFER_SIZE,
intf->rx_ring_dma_valid = intf->rx_ring_dma + RING_BUFFER_SIZE - 1;