diff --git a/Documentation/ABI/testing/sysfs-tty b/Documentation/ABI/testing/sysfs-tty
index 9eb3c2b6b040..441105a75d1f 100644
--- a/Documentation/ABI/testing/sysfs-tty
+++ b/Documentation/ABI/testing/sysfs-tty
@@ -154,3 +154,12 @@ Description:
 		 device specification. For example, when user sets 7bytes on
 		 16550A, which has 1/4/8/14 bytes trigger, the RX trigger is
 		 automatically changed to 4 bytes.
+
+What:		/sys/class/tty/ttyS0/pps_4wire
+Date:		September 2018
+Contact:	Steve Sakoman <steve@sakoman.com>
+Description:
+		 Shows/sets "4 wire" mode for the PPS input to the serial driver.
+		 For fully implemented serial ports PPS is normally provided
+		 on the DCD line. For partial "4 wire" implementations CTS is
+		 used instead of DCD.
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 80bb56facfb6..ed0133395cc7 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2664,6 +2664,57 @@ static ssize_t uart_get_attr_iomem_reg_shift(struct device *dev,
 	return snprintf(buf, PAGE_SIZE, "%d\n", tmp.iomem_reg_shift);
 }
 
+static ssize_t pps_4wire_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	struct tty_port *port = dev_get_drvdata(dev);
+	struct uart_state *state = container_of(port, struct uart_state, port);
+	struct uart_port *uport;
+	int mode = 0;
+
+	mutex_lock(&port->mutex);
+	uport = uart_port_check(state);
+	if (!uport)
+		goto out;
+
+	mode = uport->pps_4wire;
+
+out:
+	mutex_unlock(&port->mutex);
+	return sprintf(buf, mode ? "yes\n" : "no\n");
+}
+
+static ssize_t pps_4wire_store(struct device *dev,
+	struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct tty_port *port = dev_get_drvdata(dev);
+	struct uart_state *state = container_of(port, struct uart_state, port);
+	struct uart_port *uport;
+	bool mode;
+	int ret;
+
+	if (!count)
+		return -EINVAL;
+
+	ret = kstrtobool(buf, &mode);
+	if (ret < 0)
+		return ret;
+
+	mutex_lock(&port->mutex);
+	uport = uart_port_check(state);
+	if (!uport)
+		goto out;
+
+	spin_lock_irq(&uport->lock);
+	uport->pps_4wire = mode;
+	spin_unlock_irq(&uport->lock);
+
+out:
+	mutex_unlock(&port->mutex);
+	return count;
+}
+static DEVICE_ATTR_RW(pps_4wire);
+
 static DEVICE_ATTR(type, S_IRUSR | S_IRGRP, uart_get_attr_type, NULL);
 static DEVICE_ATTR(line, S_IRUSR | S_IRGRP, uart_get_attr_line, NULL);
 static DEVICE_ATTR(port, S_IRUSR | S_IRGRP, uart_get_attr_port, NULL);
@@ -2692,6 +2743,7 @@ static struct attribute *tty_dev_attrs[] = {
 	&dev_attr_io_type.attr,
 	&dev_attr_iomem_base.attr,
 	&dev_attr_iomem_reg_shift.attr,
+	&dev_attr_pps_4wire.attr,
 	NULL,
 	};
 
@@ -2748,6 +2800,9 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 		goto out;
 	}
 
+	/* assert that pps handling is done via DCD as default */
+	uport->pps_4wire = 0;
+
 	/*
 	 * If this port is a console, then the spinlock is already
 	 * initialised.
@@ -2923,7 +2978,7 @@ void uart_handle_dcd_change(struct uart_port *uport, unsigned int status)
 
 	lockdep_assert_held_once(&uport->lock);
 
-	if (tty) {
+	if (tty && !uport->pps_4wire) {
 		ld = tty_ldisc_ref(tty);
 		if (ld) {
 			if (ld->ops->dcd_change)
@@ -2952,8 +3007,21 @@ EXPORT_SYMBOL_GPL(uart_handle_dcd_change);
  */
 void uart_handle_cts_change(struct uart_port *uport, unsigned int status)
 {
+	struct tty_port *port = &uport->state->port;
+	struct tty_struct *tty = port->tty;
+	struct tty_ldisc *ld;
+
 	lockdep_assert_held_once(&uport->lock);
 
+	if (tty && uport->pps_4wire) {
+		ld = tty_ldisc_ref(tty);
+		if (ld) {
+			if (ld->ops->dcd_change)
+				ld->ops->dcd_change(tty, status);
+			tty_ldisc_deref(ld);
+		}
+	}
+
 	uport->icount.cts++;
 
 	if (uart_softcts_mode(uport)) {
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 406edae44ca3..079793e5d3fa 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -255,7 +255,8 @@ struct uart_port {
 	struct device		*dev;			/* parent device */
 	unsigned char		hub6;			/* this should be in the 8250 driver */
 	unsigned char		suspended;
-	unsigned char		unused[2];
+	unsigned char		pps_4wire;		/* CTS instead of DCD */
+	unsigned char		unused;
 	const char		*name;			/* port name */
 	struct attribute_group	*attr_group;		/* port specific attributes */
 	const struct attribute_group **tty_groups;	/* all attributes (serial core use only) */