static void pl011_stop_tx(struct uart_port *port, unsigned int tty_stop)
{
	struct uart_amba_port *uap = (struct uart_amba_port *)port;

	uap->im &= ~UART011_TXIM;  //transmit  mask  interrupt  //
	writew(uap->im, uap->port.membase + UART011_IMSC); 
                         //Imsc- interrupt mask