tty: xuartps: Add support for setting modem control signals

Add support for setting the state of the DTR and RTS signals.
Acked-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/xilinx_uartps.c

@@ -132,6 +132,15 @@ MODULE_PARM_DESC(rx_timeout, "Rx timeout, 1-255");
 /* Goes in read_status_mask for break detection as the HW doesn't do it*/
 #define CDNS_UART_IXR_BRK	0x80000000
 
+/*
+ * Modem Control register:
+ * The read/write Modem Control register controls the interface with the modem
+ * or data set, or a peripheral device emulating a modem.
+ */
+#define CDNS_UART_MODEMCR_FCM	0x00000020 /* Automatic flow control mode */
+#define CDNS_UART_MODEMCR_RTS	0x00000002 /* Request to send output control */
+#define CDNS_UART_MODEMCR_DTR	0x00000001 /* Data Terminal Ready */
+
 /*
  * Channel Status Register:
  * The channel status register (CSR) is provided to enable the control logic
@@ -915,7 +924,18 @@ static unsigned int cdns_uart_get_mctrl(struct uart_port *port)
 
 static void cdns_uart_set_mctrl(struct uart_port *port, unsigned int mctrl)
 {
-	/* N/A */
+	u32 val;
+
+	val = cdns_uart_readl(CDNS_UART_MODEMCR_OFFSET);
+
+	val &= ~(CDNS_UART_MODEMCR_RTS | CDNS_UART_MODEMCR_DTR);
+
+	if (mctrl & TIOCM_RTS)
+		val |= CDNS_UART_MODEMCR_RTS;
+	if (mctrl & TIOCM_DTR)
+		val |= CDNS_UART_MODEMCR_DTR;
+
+	cdns_uart_writel(val, CDNS_UART_MODEMCR_OFFSET);
 }
 
 #ifdef CONFIG_CONSOLE_POLL