Usage is as follows:

	myled=ledname
	tty=ttyS0

	echo tty > /sys/class/leds/$myled/trigger
	echo $tty > /sys/class/leds/$myled/ttyname

. When this new trigger is active it periodically checks the tty's
statistics and when it changed since the last check the led is flashed
once.

Signed-off-by: Uwe Kleine-König <redacted>
---
 .../ABI/testing/sysfs-class-led-trigger-tty   |   6 +
 drivers/leds/trigger/Kconfig                  |   9 +
 drivers/leds/trigger/Makefile                 |   1 +
 drivers/leds/trigger/ledtrig-tty.c            | 188 ++++++++++++++++++
 4 files changed, 204 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-class-led-trigger-tty
 create mode 100644 drivers/leds/trigger/ledtrig-tty.c

diff --git a/Documentation/ABI/testing/sysfs-class-led-trigger-tty b/Documentation/ABI/testing/sysfs-class-led-trigger-tty
new file mode 100644
index 000000000000..2bf6b24e781b
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-led-trigger-tty

@@ -0,0 +1,6 @@
+What:		/sys/class/leds/<led>/ttyname
+Date:		Dec 2020
+KernelVersion:	5.10
+Contact:	linux-leds@vger.kernel.org
+Description:
+		Specifies the tty device name of the triggering tty

diff --git a/drivers/leds/trigger/Kconfig b/drivers/leds/trigger/Kconfig
index ce9429ca6dde..b77a01bd27f4 100644
--- a/drivers/leds/trigger/Kconfig
+++ b/drivers/leds/trigger/Kconfig

@@ -144,4 +144,13 @@ config LEDS_TRIGGER_AUDIO
 	  the audio mute and mic-mute changes.
 	  If unsure, say N
 
+config LEDS_TRIGGER_TTY
+	tristate "LED Trigger for TTY devices"
+	depends on TTY
+	help
+	  This allows LEDs to be controlled by activity on ttys which includes
+	  serial devices like /dev/ttyS0.
+
+	  When build as a module this driver will be called ledtrig-tty.
+
 endif # LEDS_TRIGGERS

diff --git a/drivers/leds/trigger/Makefile b/drivers/leds/trigger/Makefile
index 733a83e2a718..25c4db97cdd4 100644
--- a/drivers/leds/trigger/Makefile
+++ b/drivers/leds/trigger/Makefile

@@ -15,3 +15,4 @@ obj-$(CONFIG_LEDS_TRIGGER_PANIC)	+= ledtrig-panic.o
 obj-$(CONFIG_LEDS_TRIGGER_NETDEV)	+= ledtrig-netdev.o
 obj-$(CONFIG_LEDS_TRIGGER_PATTERN)	+= ledtrig-pattern.o
 obj-$(CONFIG_LEDS_TRIGGER_AUDIO)	+= ledtrig-audio.o
+obj-$(CONFIG_LEDS_TRIGGER_TTY)		+= ledtrig-tty.o

diff --git a/drivers/leds/trigger/ledtrig-tty.c b/drivers/leds/trigger/ledtrig-tty.c
new file mode 100644
index 000000000000..c1e87c0d23c3
--- /dev/null
+++ b/drivers/leds/trigger/ledtrig-tty.c

@@ -0,0 +1,188 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/delay.h>
+#include <linux/leds.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <uapi/linux/serial.h>
+
+struct ledtrig_tty_data {
+	struct led_classdev *led_cdev;
+	struct delayed_work dwork;
+	struct mutex mutex;
+	const char *ttyname;
+	struct tty_struct *tty;
+	int rx, tx;
+};
+
+static void ledtrig_tty_halt(struct ledtrig_tty_data *trigger_data)
+{
+	cancel_delayed_work_sync(&trigger_data->dwork);
+}