UPF_BUG_THRE 1736 drivers/tty/serial/8250/8250_pci.c port->port.flags |= UPF_BUG_THRE; UPF_BUG_THRE 2233 drivers/tty/serial/8250/8250_port.c up->port.flags & UPF_BUG_THRE) {