count_trbs
num_trbs = count_trbs(req->dma, req->length);
return count_trbs(urb->transfer_dma, urb->transfer_buffer_length);
num_trbs += count_trbs(sg_dma_address(sg), len);
return count_trbs(addr, len);
unsigned int count_trbs(u64 addr, u64 len);