tty: xuartps: Don't consider circular buffer when enabling transmitter

Restarting the transmitter even if the circ buffer is empty may be
necessary to push out remaining data when the port is restarted after
being stopped.

Cc: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/xilinx_uartps.c

@@ -512,7 +512,7 @@ static void cdns_uart_start_tx(struct uart_port *port)
 {
 	unsigned int status, numbytes = port->fifosize;
 
-	if (uart_circ_empty(&port->state->xmit) || uart_tx_stopped(port))
+	if (uart_tx_stopped(port))
 		return;
 
 	/*
@@ -524,6 +524,9 @@ static void cdns_uart_start_tx(struct uart_port *port)
 	status |= CDNS_UART_CR_TX_EN;
 	writel(status, port->membase + CDNS_UART_CR_OFFSET);
 
+	if (uart_circ_empty(&port->state->xmit))
+		return;
+
 	while (numbytes-- && ((readl(port->membase + CDNS_UART_SR_OFFSET) &
 				CDNS_UART_SR_TXFULL)) != CDNS_UART_SR_TXFULL) {
 		/* Break if no more data available in the UART buffer */