serial: imx: repair and complete handshaking

The .get_mctrl callback should not report the status of RTS or LOOP, so
drop this. Instead implement reporting the state of CAR (aka DCD) and
RI.

For .set_mctrl implement setting the DTR line.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -148,8 +148,11 @@
 #define USR2_TXFE	 (1<<14) /* Transmit buffer FIFO empty */
 #define USR2_DTRF	 (1<<13) /* DTR edge interrupt flag */
 #define USR2_IDLE	 (1<<12) /* Idle condition */
+#define USR2_RIDELT	 (1<<10) /* Ring Interrupt Delta */
+#define USR2_RIIN	 (1<<9)	 /* Ring Indicator Input */
 #define USR2_IRINT	 (1<<8)	 /* Serial infrared interrupt flag */
 #define USR2_WAKE	 (1<<7)	 /* Wake */
+#define USR2_DCDIN	 (1<<5)	 /* Data Carrier Detect Input */
 #define USR2_RTSF	 (1<<4)	 /* RTS edge interrupt flag */
 #define USR2_TXDC	 (1<<3)	 /* Transmitter complete */
 #define USR2_BRCD	 (1<<2)	 /* Break condition */
@@ -804,16 +807,19 @@ static unsigned int imx_tx_empty(struct uart_port *port)
 static unsigned int imx_get_mctrl(struct uart_port *port)
 {
 	struct imx_port *sport = (struct imx_port *)port;
-	unsigned int tmp = TIOCM_DSR | TIOCM_CAR;
+	unsigned int tmp = TIOCM_DSR;
+	unsigned usr1 = readl(sport->port.membase + USR1);
 
-	if (readl(sport->port.membase + USR1) & USR1_RTSS)
+	if (usr1 & USR1_RTSS)
 		tmp |= TIOCM_CTS;
 
-	if (readl(sport->port.membase + UCR2) & UCR2_CTS)
-		tmp |= TIOCM_RTS;
+	/* in DCE mode DCDIN is always 0 */
+	if (!(usr1 & USR2_DCDIN))
+		tmp |= TIOCM_CAR;
 
-	if (readl(sport->port.membase + uts_reg(sport)) & UTS_LOOP)
-		tmp |= TIOCM_LOOP;
+	/* in DCE mode RIIN is always 0 */
+	if (readl(sport->port.membase + USR2) & USR2_RIIN)
+		tmp |= TIOCM_RI;
 
 	return tmp;
 }
@@ -831,6 +837,11 @@ static void imx_set_mctrl(struct uart_port *port, unsigned int mctrl)
 		writel(temp, sport->port.membase + UCR2);
 	}
 
+	temp = readl(sport->port.membase + UCR3) & ~UCR3_DSR;
+	if (!(mctrl & TIOCM_DTR))
+		temp |= UCR3_DSR;
+	writel(temp, sport->port.membase + UCR3);
+
 	temp = readl(sport->port.membase + uts_reg(sport)) & ~UTS_LOOP;
 	if (mctrl & TIOCM_LOOP)
 		temp |= UTS_LOOP;