[PATCH v6 4/4] leds: trigger: implement a tty trigger

[Uwe Kleine-KÃnig]

From: Uwe Kleine-KÃnig <u.kleine-koenig@xxxxxxxxxxxxxx>

Usage is as follows:

	myled=ledname
	tty=ttyS0

	echo tty > /sys/class/leds/$myled/trigger
	cat /sys/class/tty/$tty/dev > /sys/class/leds/$myled/dev

. 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-KÃnig <u.kleine-koenig@xxxxxxxxxxxxxx>
---
 .../ABI/testing/sysfs-class-led-trigger-tty   |   6 +
 drivers/leds/trigger/Kconfig                  |   7 +
 drivers/leds/trigger/Makefile                 |   1 +
 drivers/leds/trigger/ledtrig-tty.c            | 159 ++++++++++++++++++
 4 files changed, 173 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..f56f9721c317
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-led-trigger-tty
@@ -0,0 +1,6 @@
+What:		/sys/class/leds/<led>/dev
+Date:		Dec 2019
+KernelVersion:	5.6
+Contact:	linux-leds@xxxxxxxxxxxxxxx
+Description:
+		Specifies $major:$minor of the triggering tty
diff --git a/drivers/leds/trigger/Kconfig b/drivers/leds/trigger/Kconfig
index ce9429ca6dde..40ff08c93f56 100644
--- a/drivers/leds/trigger/Kconfig
+++ b/drivers/leds/trigger/Kconfig
@@ -144,4 +144,11 @@ 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.
+
 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..e1be93c3026f
--- /dev/null
+++ b/drivers/leds/trigger/ledtrig-tty.c
@@ -0,0 +1,159 @@
+// 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 tty_struct *tty;
+	dev_t device;
+	int rx, tx;
+};
+
+static void ledtrig_tty_halt(struct ledtrig_tty_data *trigger_data)
+{
+	cancel_delayed_work_sync(&trigger_data->dwork);
+}
+
+static void ledtrig_tty_restart(struct ledtrig_tty_data *trigger_data)
+{
+	schedule_delayed_work(&trigger_data->dwork, 0);
+}
+
+static ssize_t dev_show(struct device *dev,
+			struct device_attribute *attr, char *buf)
+{
+	struct ledtrig_tty_data *trigger_data = led_trigger_get_drvdata(dev);
+	ssize_t len = 0;
+
+	if (trigger_data->tty)
+		len = sprintf(buf, "%d:%d\n", MAJOR(trigger_data->device),
+			      MINOR(trigger_data->device));
+
+	return len;
+}
+
+static ssize_t dev_store(struct device *dev,
+			 struct device_attribute *attr, const char *buf,
+			 size_t size)
+{
+	struct ledtrig_tty_data *trigger_data = led_trigger_get_drvdata(dev);
+	struct tty_struct *tty;
+	dev_t d;
+	int ret;
+
+	if (size == 0 || (size == 1 && buf[0] == '\n')) {
+		tty = NULL;
+	} else {
+		ret = kstrtodev_t(buf, &d);
+		if (ret < 0)
+			return ret;
+
+		tty = tty_kopen_shared(d);
+		if (IS_ERR(tty))
+			return PTR_ERR(tty);
+	}
+
+	ledtrig_tty_halt(trigger_data);
+
+	tty_kref_put(trigger_data->tty);
+	trigger_data->tty = tty;
+	trigger_data->device = d;
+
+	if (tty) {
+		struct serial_icounter_struct icount;
+		ret = tty_get_icount(trigger_data->tty, &icount);
+		if (!ret) {
+			trigger_data->tx = icount.tx;
+			trigger_data->rx = icount.rx;
+		}
+
+		ledtrig_tty_restart(trigger_data);
+	}
+
+	return size;
+}
+static DEVICE_ATTR_RW(dev);
+
+static void ledtrig_tty_work(struct work_struct *work)
+{
+	struct ledtrig_tty_data *trigger_data =
+		container_of(work, struct ledtrig_tty_data, dwork.work);
+	struct serial_icounter_struct icount;
+	int ret;
+
+	if (!trigger_data->tty) {
+		led_set_brightness(trigger_data->led_cdev, LED_OFF);
+		return;
+	}
+
+	ret = tty_get_icount(trigger_data->tty, &icount);
+	if (ret)
+		return;
+
+	while (icount.rx != trigger_data->rx ||
+	       icount.tx != trigger_data->tx) {
+		led_set_brightness(trigger_data->led_cdev, LED_ON);
+
+		msleep(100);
+
+		led_set_brightness(trigger_data->led_cdev, LED_OFF);
+
+		trigger_data->rx = icount.rx;
+		trigger_data->tx = icount.tx;
+
+		ret = tty_get_icount(trigger_data->tty, &icount);
+		if (ret)
+			return;
+	}
+
+	schedule_delayed_work(&trigger_data->dwork, msecs_to_jiffies(100));
+}
+
+static struct attribute *ledtrig_tty_attrs[] = {
+	&dev_attr_dev.attr,
+	NULL
+};
+ATTRIBUTE_GROUPS(ledtrig_tty);
+
+static int ledtrig_tty_activate(struct led_classdev *led_cdev)
+{
+	struct ledtrig_tty_data *trigger_data;
+
+	trigger_data = kzalloc(sizeof(*trigger_data), GFP_KERNEL);
+	if (!trigger_data)
+		return -ENOMEM;
+
+	led_set_trigger_data(led_cdev, trigger_data);
+
+	INIT_DELAYED_WORK(&trigger_data->dwork, ledtrig_tty_work);
+	trigger_data->led_cdev = led_cdev;
+
+	return 0;
+}
+
+static void ledtrig_tty_deactivate(struct led_classdev *led_cdev)
+{
+	struct ledtrig_tty_data *trigger_data = led_get_trigger_data(led_cdev);
+
+	cancel_delayed_work_sync(&trigger_data->dwork);
+
+	kfree(trigger_data);
+}
+
+struct led_trigger ledtrig_tty = {
+	.name = "tty",
+	.activate = ledtrig_tty_activate,
+	.deactivate = ledtrig_tty_deactivate,
+	.groups = ledtrig_tty_groups,
+};
+module_led_trigger(ledtrig_tty);
+
+MODULE_AUTHOR("Uwe Kleine-KÃnig <u.kleine-koenig@xxxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("UART LED trigger");
+MODULE_LICENSE("GPL v2");
-- 
2.24.0