[PATCH v8 2/3] trigger: ledtrig-tty: add additional modes

[Florian Eckert]

Add additional modes to trigger the selected LED.
The following modes are supported:

Tx/Rx:	Flash LED on data transmission (default)
CTS:	DCE Ready to accept data from the DTE.
DSR:	DCE is ready to receive and send data.
CAR:	DCE is receiving a carrier from a remote DTE.
RNG:	DCE has detected an incoming ring signal.

The mode can be changed for example with the following command:
echo "CTS" > /sys/class/leds/<led>/mode

This would turn on the LED, when the DTE(modem) signals the DCE that it
is ready to accept data.

Signed-off-by: Florian Eckert <fe@xxxxxxxxxx>
---
 .../ABI/testing/sysfs-class-led-trigger-tty   |  18 +++
 drivers/leds/trigger/ledtrig-tty.c            | 143 ++++++++++++++++--
 2 files changed, 146 insertions(+), 15 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-class-led-trigger-tty b/Documentation/ABI/testing/sysfs-class-led-trigger-tty
index 2bf6b24e781b..2e4e4c009a21 100644
--- a/Documentation/ABI/testing/sysfs-class-led-trigger-tty
+++ b/Documentation/ABI/testing/sysfs-class-led-trigger-tty
@@ -4,3 +4,21 @@ KernelVersion:	5.10
 Contact:	linux-leds@xxxxxxxxxxxxxxx
 Description:
 		Specifies the tty device name of the triggering tty
+
+What:		/sys/class/leds/<led>/mode
+Date:		January 2023
+KernelVersion:	6.3
+Description:
+		Specifies the mode to trigger the LED.
+		The following operating modes are supported:
+
+		=====  ============================================
+		Tx/Rx  Flash LED on data transmission (default)
+		CTS    DCE Ready to accept data from the DTE
+		DSR    DCE is ready to receive and send data
+		CAR    DCE is receiving a carrier from a remote DTE
+		RNG    DCE has detected an incoming ring signal
+		=====  ============================================
+
+		In CTS/DSR/CAR/RNG modes, the LED is enabled when the
+		tty line is high.
\ No newline at end of file
diff --git a/drivers/leds/trigger/ledtrig-tty.c b/drivers/leds/trigger/ledtrig-tty.c
index f62db7e520b5..d3407830fa69 100644
--- a/drivers/leds/trigger/ledtrig-tty.c
+++ b/drivers/leds/trigger/ledtrig-tty.c
@@ -7,6 +7,15 @@
 #include <linux/tty.h>
 #include <uapi/linux/serial.h>
 
+enum tty_led_mode {
+	TTY_LED_RXTX,
+	TTY_LED_CTS,
+	TTY_LED_DSR,
+	TTY_LED_CAR,
+	TTY_LED_RNG,
+	_TTY_LED_LAST = TTY_LED_RNG
+};
+
 struct ledtrig_tty_data {
 	struct led_classdev *led_cdev;
 	struct delayed_work dwork;
@@ -14,6 +23,15 @@ struct ledtrig_tty_data {
 	const char *ttyname;
 	struct tty_struct *tty;
 	int rx, tx;
+	enum tty_led_mode mode;
+};
+
+static const char * const mode[] = {
+	[TTY_LED_RXTX] = "Tx/Rx", /* Transmit and Receive data */
+	[TTY_LED_CTS] = "CTS", /* CTS clear to send */
+	[TTY_LED_DSR] = "DSR", /* DSR data set ready */
+	[TTY_LED_CAR] = "CAR", /* CAR data carrier detect (DCD) */
+	[TTY_LED_RNG] = "RNG", /* RNG ring indicator */
 };
 
 static void ledtrig_tty_restart(struct ledtrig_tty_data *trigger_data)
@@ -21,6 +39,70 @@ static void ledtrig_tty_restart(struct ledtrig_tty_data *trigger_data)
 	schedule_delayed_work(&trigger_data->dwork, 0);
 }
 
+static ssize_t ledtrig_tty_mode_show(char *buf, enum tty_led_mode tty_mode)
+{
+	int len = 0;
+	int i;
+
+	for (i = 0; i <= _TTY_LED_LAST; i++) {
+		bool hit = tty_mode == i;
+		bool last = i == _TTY_LED_LAST;
+
+		len += sysfs_emit_at(buf, len, "%s%s%s%s",
+				  hit ? "[" : "",
+				  mode[i],
+				  hit ? "]" : "",
+				  last ? "" : " ");
+	}
+
+	len += sysfs_emit_at(buf, len, "\n");
+
+	return len;
+}
+
+static ssize_t tty_led_mode_show(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	struct ledtrig_tty_data *trigger_data = led_trigger_get_drvdata(dev);
+	enum tty_led_mode tty_mode;
+
+	mutex_lock(&trigger_data->mutex);
+	tty_mode = trigger_data->mode;
+	mutex_unlock(&trigger_data->mutex);
+
+	return ledtrig_tty_mode_show(buf, tty_mode);
+}
+
+static ssize_t tty_led_mode_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);
+	ssize_t ret = size;
+	int i;
+	enum tty_led_mode tty_mode = _TTY_LED_LAST;
+
+	/* Check for new line in string */
+	if (size > 0 && buf[size - 1] == '\n')
+		size -= 1;
+
+	for (i = 0; i <= _TTY_LED_LAST; i++)
+		if (strncmp(buf, mode[i], size) == 0) {
+			tty_mode = i;
+			break;
+		}
+
+	if (i > _TTY_LED_LAST)
+		return -EINVAL;
+
+	mutex_lock(&trigger_data->mutex);
+	trigger_data->mode = tty_mode;
+	mutex_unlock(&trigger_data->mutex);
+
+	return ret;
+}
+static DEVICE_ATTR_RW(tty_led_mode);
+
 static ssize_t ttyname_show(struct device *dev,
 			    struct device_attribute *attr, char *buf)
 {
@@ -76,6 +158,17 @@ static ssize_t ttyname_store(struct device *dev,
 }
 static DEVICE_ATTR_RW(ttyname);
 
+static void ledtrig_tty_flags(struct ledtrig_tty_data *trigger_data, unsigned int flag)
+{
+	unsigned int status;
+
+	status = tty_get_mget(trigger_data->tty);
+	if (status & flag)
+		led_set_brightness_sync(trigger_data->led_cdev, LED_ON);
+	else
+		led_set_brightness_sync(trigger_data->led_cdev, LED_OFF);
+}
+
 static void ledtrig_tty_work(struct work_struct *work)
 {
 	struct ledtrig_tty_data *trigger_data =
@@ -113,21 +206,37 @@ static void ledtrig_tty_work(struct work_struct *work)
 		trigger_data->tty = tty;
 	}
 
-	ret = tty_get_icount(trigger_data->tty, &icount);
-	if (ret) {
-		dev_info(trigger_data->tty->dev, "Failed to get icount, stopped polling\n");
-		mutex_unlock(&trigger_data->mutex);
-		return;
-	}
-
-	if (icount.rx != trigger_data->rx ||
-	    icount.tx != trigger_data->tx) {
-		led_set_brightness_sync(trigger_data->led_cdev, LED_ON);
-
-		trigger_data->rx = icount.rx;
-		trigger_data->tx = icount.tx;
-	} else {
-		led_set_brightness_sync(trigger_data->led_cdev, LED_OFF);
+	switch (trigger_data->mode) {
+	case TTY_LED_CTS:
+		ledtrig_tty_flags(trigger_data, TIOCM_CTS);
+		break;
+	case TTY_LED_DSR:
+		ledtrig_tty_flags(trigger_data, TIOCM_DSR);
+		break;
+	case TTY_LED_CAR:
+		ledtrig_tty_flags(trigger_data, TIOCM_CAR);
+		break;
+	case TTY_LED_RNG:
+		ledtrig_tty_flags(trigger_data, TIOCM_RNG);
+		break;
+	case TTY_LED_RXTX:
+	default:
+		ret = tty_get_icount(trigger_data->tty, &icount);
+		if (ret) {
+			dev_info(trigger_data->tty->dev, "Failed to get icount, stopped polling\n");
+			mutex_unlock(&trigger_data->mutex);
+			return;
+		}
+
+		if (icount.rx != trigger_data->rx || icount.tx != trigger_data->tx) {
+			led_set_brightness_sync(trigger_data->led_cdev, LED_ON);
+
+			trigger_data->rx = icount.rx;
+			trigger_data->tx = icount.tx;
+		} else {
+			led_set_brightness_sync(trigger_data->led_cdev, LED_OFF);
+		}
+		break;
 	}
 
 out:
@@ -137,6 +246,7 @@ static void ledtrig_tty_work(struct work_struct *work)
 
 static struct attribute *ledtrig_tty_attrs[] = {
 	&dev_attr_ttyname.attr,
+	&dev_attr_tty_led_mode.attr,
 	NULL
 };
 ATTRIBUTE_GROUPS(ledtrig_tty);
@@ -149,6 +259,9 @@ static int ledtrig_tty_activate(struct led_classdev *led_cdev)
 	if (!trigger_data)
 		return -ENOMEM;
 
+	/* Set default mode */
+	trigger_data->mode = TTY_LED_RXTX;
+
 	led_set_trigger_data(led_cdev, trigger_data);
 
 	INIT_DELAYED_WORK(&trigger_data->dwork, ledtrig_tty_work);
-- 
2.30.2