serial: max310x: turn off transmitter before activating AutoCTS or auto transmitter flow control

As documented in the data-sheet, the transmitter must be disabled before
activating AutoCTS or auto transmitter flow control. Accordingly, the
transmitter must be enabled after AutoCTS or auto transmitter flow
control gets deactivated.

Signed-off-by: Christoph Vogtländer <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/max310x.c

···
 	max310x_port_write(port, MAX310X_XON1_REG, termios->c_cc[VSTART]);
 	max310x_port_write(port, MAX310X_XOFF1_REG, termios->c_cc[VSTOP]);
 
+	/* Disable transmitter before enabling AutoCTS or auto transmitter
+	 * flow control
+	 */
+	if (termios->c_cflag & CRTSCTS || termios->c_iflag & IXOFF) {
+		max310x_port_update(port, MAX310X_MODE1_REG,
+				    MAX310X_MODE1_TXDIS_BIT,
+				    MAX310X_MODE1_TXDIS_BIT);
+	}
+
 	port->status &= ~(UPSTAT_AUTOCTS | UPSTAT_AUTORTS | UPSTAT_AUTOXOFF);
 
 	if (termios->c_cflag & CRTSCTS) {
···
 			MAX310X_FLOWCTRL_SWFLOWEN_BIT;
 	}
 	max310x_port_write(port, MAX310X_FLOWCTRL_REG, flow);
+
+	/* Enable transmitter after disabling AutoCTS and auto transmitter
+	 * flow control
+	 */
+	if (!(termios->c_cflag & CRTSCTS) && !(termios->c_iflag & IXOFF)) {
+		max310x_port_update(port, MAX310X_MODE1_REG,
+				    MAX310X_MODE1_TXDIS_BIT,
+				    0);
+	}
 
 	/* Get baud rate generator configuration */
 	baud = uart_get_baud_rate(port, termios, old,