serial: imx: add CREAD flag support

Add CREAD flag hanlding in set_termios and UART DMA mode
which ignores all received chars when CREAD flag cleared.
Signed-off-by: Jiada Wang <jiada_wang@mentor.com>
Signed-off-by: Anton Bondarenko <anton_bondarenko@mentor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -74,6 +74,7 @@
 #define IMX21_UTS 0xb4 /* UART Test Register on all other i.mx*/
 
 /* UART Control Register Bit Fields.*/
+#define URXD_DUMMY_READ (1<<16)
 #define URXD_CHARRDY	(1<<15)
 #define URXD_ERR	(1<<14)
 #define URXD_OVRRUN	(1<<13)
@@ -710,6 +711,9 @@ static irqreturn_t imx_rxint(int irq, void *dev_id)
 #endif
 		}
 
+		if (sport->port.ignore_status_mask & URXD_DUMMY_READ)
+			goto out;
+
 		tty_insert_flip_char(port, rx, flg);
 	}
 
@@ -910,6 +914,7 @@ static void dma_rx_callback(void *data)
 	dev_dbg(sport->port.dev, "We get %d bytes.\n", count);
 
 	if (count) {
+		if (!(sport->port.ignore_status_mask & URXD_DUMMY_READ))
 			tty_insert_flip_string(port, sport->rx_buf, count);
 		tty_flip_buffer_push(port);
 
@@ -1330,6 +1335,9 @@ imx_set_termios(struct uart_port *port, struct ktermios *termios,
 			sport->port.ignore_status_mask |= URXD_OVRRUN;
 	}
 
+	if ((termios->c_cflag & CREAD) == 0)
+		sport->port.ignore_status_mask |= URXD_DUMMY_READ;
+
 	/*
 	 * Update the per-port timeout.
 	 */