serial: max310x: Properly set flags in AutoCTS mode

Commit 391f93f2 ("serial: core: Rework hw-assisted flow control
support") has changed the way the AutoCTS mode is handled.

According to that change, serial drivers which enable H/W AutoCTS mode must
set UPSTAT_AUTORTS, UPSTAT_AUTOCTS and UPSTAT_AUTOXOFF to prevent the
serial core from inadvertently disabling RX or TX. This patch adds proper
handling of UPSTAT_AUTORTS, UPSTAT_AUTOCTS and UPSTAT_AUTOXOFF flags.
Signed-off-by: Christoph Vogtländer <c.vogtlaender@sigma-surface-science.com>
Link: https://lore.kernel.org/r/20190904121141.4570-1-c.vogtlaender@sigma-surface-science.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/max310x.c

@@ -955,15 +955,23 @@ static void max310x_set_termios(struct uart_port *port,
 	/* Configure flow control */
 	max310x_port_write(port, MAX310X_XON1_REG, termios->c_cc[VSTART]);
 	max310x_port_write(port, MAX310X_XOFF1_REG, termios->c_cc[VSTOP]);
-	if (termios->c_cflag & CRTSCTS)
+
+	port->status &= ~(UPSTAT_AUTOCTS | UPSTAT_AUTORTS | UPSTAT_AUTOXOFF);
+
+	if (termios->c_cflag & CRTSCTS) {
+		/* Enable AUTORTS and AUTOCTS */
+		port->status |= UPSTAT_AUTOCTS | UPSTAT_AUTORTS;
 		flow |= MAX310X_FLOWCTRL_AUTOCTS_BIT |
 			MAX310X_FLOWCTRL_AUTORTS_BIT;
+	}
 	if (termios->c_iflag & IXON)
 		flow |= MAX310X_FLOWCTRL_SWFLOW3_BIT |
 			MAX310X_FLOWCTRL_SWFLOWEN_BIT;
-	if (termios->c_iflag & IXOFF)
+	if (termios->c_iflag & IXOFF) {
+		port->status |= UPSTAT_AUTOXOFF;
 		flow |= MAX310X_FLOWCTRL_SWFLOW1_BIT |
 			MAX310X_FLOWCTRL_SWFLOWEN_BIT;
+	}
 	max310x_port_write(port, MAX310X_FLOWCTRL_REG, flow);
 
 	/* Get baud rate generator configuration */