diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index 11e05aa014e5..b861585ca02a 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -374,6 +374,7 @@ static inline int is_omap1510_8250(struct uart_8250_port *pt)
 
 #ifdef CONFIG_SERIAL_8250_DMA
 extern int serial8250_tx_dma(struct uart_8250_port *);
+extern void serial8250_tx_dma_flush(struct uart_8250_port *);
 extern int serial8250_rx_dma(struct uart_8250_port *);
 extern void serial8250_rx_dma_flush(struct uart_8250_port *);
 extern int serial8250_request_dma(struct uart_8250_port *);
@@ -406,6 +407,7 @@ static inline int serial8250_tx_dma(struct uart_8250_port *p)
 {
 	return -1;
 }
+static inline void serial8250_tx_dma_flush(struct uart_8250_port *p) { }
 static inline int serial8250_rx_dma(struct uart_8250_port *p)
 {
 	return -1;
diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c
index d215c494ee24..f245a84f4a50 100644
--- a/drivers/tty/serial/8250/8250_dma.c
+++ b/drivers/tty/serial/8250/8250_dma.c
@@ -149,6 +149,22 @@ int serial8250_tx_dma(struct uart_8250_port *p)
 	return ret;
 }
 
+void serial8250_tx_dma_flush(struct uart_8250_port *p)
+{
+	struct uart_8250_dma *dma = p->dma;
+
+	if (!dma->tx_running)
+		return;
+
+	/*
+	 * kfifo_reset() has been called by the serial core, avoid
+	 * advancing and underflowing in __dma_tx_complete().
+	 */
+	dma->tx_size = 0;
+
+	dmaengine_terminate_async(dma->rxchan);
+}
+
 int serial8250_rx_dma(struct uart_8250_port *p)
 {
 	struct uart_8250_dma		*dma = p->dma;
diff --git a/drivers/tty/serial/8250/8250_of.c b/drivers/tty/serial/8250/8250_of.c
index 64aed7efc569..11c860ea80f6 100644
--- a/drivers/tty/serial/8250/8250_of.c
+++ b/drivers/tty/serial/8250/8250_of.c
@@ -110,7 +110,6 @@ static int of_platform_serial_setup(struct platform_device *ofdev,
 	spin_lock_init(&port->lock);
 
 	if (resource_type(&resource) == IORESOURCE_IO) {
-		port->iotype = UPIO_PORT;
 		port->iobase = resource.start;
 	} else {
 		port->mapbase = resource.start;
diff --git a/drivers/tty/serial/8250/8250_platform.c b/drivers/tty/serial/8250/8250_platform.c
index 8bdc1879d952..c0343bfb8064 100644
--- a/drivers/tty/serial/8250/8250_platform.c
+++ b/drivers/tty/serial/8250/8250_platform.c
@@ -112,7 +112,6 @@ static int serial8250_probe_acpi(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	struct uart_8250_port uart = { };
 	struct resource *regs;
-	unsigned char iotype;
 	int ret, line;
 
 	regs = platform_get_mem_or_io(pdev, 0);
@@ -122,13 +121,11 @@ static int serial8250_probe_acpi(struct platform_device *pdev)
 	switch (resource_type(regs)) {
 	case IORESOURCE_IO:
 		uart.port.iobase = regs->start;
-		iotype = UPIO_PORT;
 		break;
 	case IORESOURCE_MEM:
 		uart.port.mapbase = regs->start;
 		uart.port.mapsize = resource_size(regs);
 		uart.port.flags = UPF_IOREMAP;
-		iotype = UPIO_MEM;
 		break;
 	default:
 		return -EINVAL;
@@ -147,12 +144,6 @@ static int serial8250_probe_acpi(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
-	/*
-	 * The previous call may not set iotype correctly when reg-io-width
-	 * property is absent and it doesn't support IO port resource.
-	 */
-	uart.port.iotype = iotype;
-
 	line = serial8250_register_8250_port(&uart);
 	if (line < 0)
 		return line;
diff --git a/drivers/tty/serial/8250/8250_pnp.c b/drivers/tty/serial/8250/8250_pnp.c
index 7c06ae79d8e2..7a837fdf9df1 100644
--- a/drivers/tty/serial/8250/8250_pnp.c
+++ b/drivers/tty/serial/8250/8250_pnp.c
@@ -436,7 +436,6 @@ serial_pnp_probe(struct pnp_dev *dev, const struct pnp_device_id *dev_id)
 {
 	struct uart_8250_port uart, *port;
 	int ret, flags = dev_id->driver_data;
-	unsigned char iotype;
 	long line;
 
 	if (flags & UNKNOWN_DEV) {
@@ -448,14 +447,11 @@ serial_pnp_probe(struct pnp_dev *dev, const struct pnp_device_id *dev_id)
 	memset(&uart, 0, sizeof(uart));
 	if ((flags & CIR_PORT) && pnp_port_valid(dev, 2)) {
 		uart.port.iobase = pnp_port_start(dev, 2);
-		iotype = UPIO_PORT;
 	} else if (pnp_port_valid(dev, 0)) {
 		uart.port.iobase = pnp_port_start(dev, 0);
-		iotype = UPIO_PORT;
 	} else if (pnp_mem_valid(dev, 0)) {
 		uart.port.mapbase = pnp_mem_start(dev, 0);
 		uart.port.mapsize = pnp_mem_len(dev, 0);
-		iotype = UPIO_MEM;
 		uart.port.flags = UPF_IOREMAP;
 	} else
 		return -ENODEV;
@@ -471,12 +467,6 @@ serial_pnp_probe(struct pnp_dev *dev, const struct pnp_device_id *dev_id)
 	if (ret)
 		return ret;
 
-	/*
-	 * The previous call may not set iotype correctly when reg-io-width
-	 * property is absent and it doesn't support IO port resource.
-	 */
-	uart.port.iotype = iotype;
-
 	if (flags & CIR_PORT) {
 		uart.port.flags |= UPF_FIXED_PORT | UPF_FIXED_TYPE;
 		uart.port.type = PORT_8250_CIR;
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index d7976a21cca9..442967a6cd52 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2555,6 +2555,14 @@ static void serial8250_shutdown(struct uart_port *port)
 		serial8250_do_shutdown(port);
 }
 
+static void serial8250_flush_buffer(struct uart_port *port)
+{
+	struct uart_8250_port *up = up_to_u8250p(port);
+
+	if (up->dma)
+		serial8250_tx_dma_flush(up);
+}
+
 static unsigned int serial8250_do_get_divisor(struct uart_port *port,
 					      unsigned int baud,
 					      unsigned int *frac)
@@ -3244,6 +3252,7 @@ static const struct uart_ops serial8250_pops = {
 	.break_ctl	= serial8250_break_ctl,
 	.startup	= serial8250_startup,
 	.shutdown	= serial8250_shutdown,
+	.flush_buffer	= serial8250_flush_buffer,
 	.set_termios	= serial8250_set_termios,
 	.set_ldisc	= serial8250_set_ldisc,
 	.pm		= serial8250_pm,
diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index 7b51cdc274fd..560f45ed19ae 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -1561,7 +1561,7 @@ int sc16is7xx_probe(struct device *dev, const struct sc16is7xx_devtype *devtype,
 	/* Always ask for fixed clock rate from a property. */
 	device_property_read_u32(dev, "clock-frequency", &uartclk);
 
-	s->polling = !!irq;
+	s->polling = (irq <= 0);
 	if (s->polling)
 		dev_dbg(dev,
 			"No interrupt pin definition, falling back to polling mode\n");
diff --git a/drivers/tty/serial/serial_port.c b/drivers/tty/serial/serial_port.c
index d35f1d24156c..2fc48cd63f6c 100644
--- a/drivers/tty/serial/serial_port.c
+++ b/drivers/tty/serial/serial_port.c
@@ -173,6 +173,7 @@ EXPORT_SYMBOL(uart_remove_one_port);
  * The caller is responsible to initialize the following fields of the @port
  *   ->dev (must be valid)
  *   ->flags
+ *   ->iobase
  *   ->mapbase
  *   ->mapsize
  *   ->regshift (if @use_defaults is false)
@@ -214,7 +215,7 @@ static int __uart_read_properties(struct uart_port *port, bool use_defaults)
 	/* Read the registers I/O access type (default: MMIO 8-bit) */
 	ret = device_property_read_u32(dev, "reg-io-width", &value);
 	if (ret) {
-		port->iotype = UPIO_MEM;
+		port->iotype = port->iobase ? UPIO_PORT : UPIO_MEM;
 	} else {
 		switch (value) {
 		case 1:
@@ -227,15 +228,16 @@ static int __uart_read_properties(struct uart_port *port, bool use_defaults)
 			port->iotype = device_is_big_endian(dev) ? UPIO_MEM32BE : UPIO_MEM32;
 			break;
 		default:
-			if (!use_defaults) {
-				dev_err(dev, "Unsupported reg-io-width (%u)\n", value);
-				return -EINVAL;
-			}
 			port->iotype = UPIO_UNKNOWN;
 			break;
 		}
 	}
 
+	if (!use_defaults && port->iotype == UPIO_UNKNOWN) {
+		dev_err(dev, "Unsupported reg-io-width (%u)\n", value);
+		return -EINVAL;
+	}
+
 	/* Read the address mapping base offset (default: no offset) */
 	ret = device_property_read_u32(dev, "reg-offset", &value);
 	if (ret)