atmel_serial: RS485: receiving enabled when sending data

By default the atmel_serial driver in RS485 mode disables receiving data until
all data in the send buffer has been sent. This flag allows to receive data
even whilst sending data.
Signed-off-by: Bernhard Roth <br@pwrnet.de>
Signed-off-by: Claudio Scordino <claudio@evidence.eu.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

Documentation/serial/serial-rs485.txt

@@ -104,6 +104,9 @@
 	rs485conf.flags |= SER_RS485_RTS_AFTER_SEND;
 	rs485conf.delay_rts_after_send = ...;
 
+	/* Set this flag if you want to receive data even whilst sending data */
+	rs485conf.flags |= SER_RS485_RX_DURING_TX;
+
 	if (ioctl (fd, TIOCSRS485, &rs485conf) < 0) {
 		/* Error handling. See errno. */
 	}

drivers/tty/serial/atmel_serial.c

@@ -339,7 +339,8 @@ static void atmel_stop_tx(struct uart_port *port)
 	/* Disable interrupts */
 	UART_PUT_IDR(port, atmel_port->tx_done_mask);
 
-	if (atmel_port->rs485.flags & SER_RS485_ENABLED)
+	if ((atmel_port->rs485.flags & SER_RS485_ENABLED) &&
+	    !(atmel_port->rs485.flags & SER_RS485_RX_DURING_TX))
 		atmel_start_rx(port);
 }
 
@@ -356,7 +357,8 @@ static void atmel_start_tx(struct uart_port *port)
 			   really need this.*/
 			return;
 
-		if (atmel_port->rs485.flags & SER_RS485_ENABLED)
+		if ((atmel_port->rs485.flags & SER_RS485_ENABLED) &&
+		    !(atmel_port->rs485.flags & SER_RS485_RX_DURING_TX))
 			atmel_stop_rx(port);
 
 		/* re-enable PDC transmit */
@@ -680,7 +682,8 @@ static void atmel_tx_dma(struct uart_port *port)
 		/* Enable interrupts */
 		UART_PUT_IER(port, atmel_port->tx_done_mask);
 	} else {
-		if (atmel_port->rs485.flags & SER_RS485_ENABLED) {
+		if ((atmel_port->rs485.flags & SER_RS485_ENABLED) &&
+		    !(atmel_port->rs485.flags & SER_RS485_RX_DURING_TX)) {
 			/* DMA done, stop TX, start RX for RS485 */
 			atmel_start_rx(port);
 		}

include/linux/serial.h

@@ -211,6 +211,7 @@ struct serial_rs485 {
 #define SER_RS485_RTS_ON_SEND		(1 << 1)
 #define SER_RS485_RTS_AFTER_SEND	(1 << 2)
 #define SER_RS485_RTS_BEFORE_SEND	(1 << 3)
+#define SER_RS485_RX_DURING_TX		(1 << 4)
 	__u32	delay_rts_before_send;	/* Milliseconds */
 	__u32	delay_rts_after_send;	/* Milliseconds */
 	__u32	padding[5];		/* Memory is cheap, new structs