tty: serial: exar: generalize RS485 setup

Move the non-board-specific part of the RS485 initialization from
iot2040_rs485_config function to a new generic function used also for
other boards.
This allows using TIOCGRS485 and TIOCSRS485 on boards (such as mPCIe
serial IO modules) which are hard-wired to RS485 or have jumpers for
their configurations.
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_exar.c

@@ -272,8 +272,32 @@ static int xr17v35x_register_gpio(struct pci_dev *pcidev,
 	return 0;
 }
 
+static int generic_rs485_config(struct uart_port *port,
+				struct serial_rs485 *rs485)
+{
+	bool is_rs485 = !!(rs485->flags & SER_RS485_ENABLED);
+	u8 __iomem *p = port->membase;
+	u8 value;
+
+	value = readb(p + UART_EXAR_FCTR);
+	if (is_rs485)
+		value |= UART_FCTR_EXAR_485;
+	else
+		value &= ~UART_FCTR_EXAR_485;
+
+	writeb(value, p + UART_EXAR_FCTR);
+
+	if (is_rs485)
+		writeb(UART_EXAR_RS485_DLY(4), p + UART_MSR);
+
+	port->rs485 = *rs485;
+
+	return 0;
+}
+
 static const struct exar8250_platform exar8250_default_platform = {
 	.register_gpio = xr17v35x_register_gpio,
+	.rs485_config = generic_rs485_config,
 };
 
 static int iot2040_rs485_config(struct uart_port *port,
@@ -306,19 +330,7 @@ static int iot2040_rs485_config(struct uart_port *port,
 	value |= mode;
 	writeb(value, p + UART_EXAR_MPIOLVL_7_0);
 
-	value = readb(p + UART_EXAR_FCTR);
-	if (is_rs485)
-		value |= UART_FCTR_EXAR_485;
-	else
-		value &= ~UART_FCTR_EXAR_485;
-	writeb(value, p + UART_EXAR_FCTR);
-
-	if (is_rs485)
-		writeb(UART_EXAR_RS485_DLY(4), p + UART_MSR);
-
-	port->rs485 = *rs485;
-
-	return 0;
+	return generic_rs485_config(port, rs485);
 }
 
 static const struct property_entry iot2040_gpio_properties[] = {