NTB_DB_READ
return ((NTB_DB_READ(device_get_parent(ntb)) >> nc->dboff)
#define NTB_REGFLAGS_MASK (NTB_REGSZ_MASK | NTB_DB_READ | NTB_PCI_REG)
NTB_REG_64 | NTB_DB_READ | ntb->self_reg->db_mask,
NTB_REG_64 | NTB_DB_READ | ntb->self_reg->db_bell,
db = (arg2 & NTB_DB_READ) != 0;