leds: ledtrig-tty: Add additional line state evaluation

The serial tty interface also supports additional input signals, that
can also be evaluated within this trigger. This change is adding the
following additional input sources, which could be controlled
via the '/sys/class/<leds>/' sysfs interface.

Explanation:
DCE = Data Communication Equipment (Modem)
DTE = Data Terminal Equipment (Computer)

- cts:
DCE is ready to accept data from the DTE (CTS = Clear To Send). If
the line state is detected, the LED is switched on.
If set to 0 (default), the LED will not evaluate CTS.
If set to 1, the LED will evaluate CTS.

- dsr:
DCE is ready to receive and send data (DSR = Data Set Ready). If the
line state is detected, the LED is switched on.
If set to 0 (default), the LED will not evaluate DSR.
If set to 1, the LED will evaluate DSR.

- dcd:
DTE is receiving a carrier from the DCE (DCD = Data Carrier Detect).
If the line state is detected, the LED is switched on.
If set to 0 (default), the LED will not evaluate DCD.
If set to 1, the LED will evaluate DCD.

- rng:
DCE has detected an incoming ring signal on the telephone line
(RNG = Ring Indicator). If the line state is detected, the LED is
switched on.
If set to 0 (default), the LED will not evaluate RNG.
If set to 1, the LED will evaluate RNG.

Also add an invert flag on LED blink, so that the LED blinks in the
correct order.

* If one off the new enabled input signals are evaluatet as 'enabled',
and data are transmitted, then the LED should first blink 'off' and
then 'on' (invert).
* If all the new enabled input signals are evaluatet as 'disabled',
and data are transmitted, then the LED should first blink 'on' and
then 'off'.

Signed-off-by: Florian Eckert <[e-mail]>
Reviewed-by: Maarten Brock <[e-mail]>
Reviewed-by: Greg Kroah-Hartman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

Documentation/ABI/testing/sysfs-class-led-trigger-tty

···
 		Signal transmission (tx) of data on the named tty device.
 		If set to 0, the LED will not blink on transmission.
 		If set to 1 (default), the LED will blink on transmission.
+
+What:		/sys/class/leds/<led>/cts
+Date:		February 2024
+KernelVersion:	6.8
+Description:
+		CTS = Clear To Send
+		DCE is ready to accept data from the DTE.
+		If the line state is detected, the LED is switched on.
+		If set to 0 (default), the LED will not evaluate CTS.
+		If set to 1, the LED will evaluate CTS.
+
+What:		/sys/class/leds/<led>/dsr
+Date:		February 2024
+KernelVersion:	6.8
+Description:
+		DSR = Data Set Ready
+		DCE is ready to receive and send data.
+		If the line state is detected, the LED is switched on.
+		If set to 0 (default), the LED will not evaluate DSR.
+		If set to 1, the LED will evaluate DSR.
+
+What:		/sys/class/leds/<led>/dcd
+Date:		February 2024
+KernelVersion:	6.8
+Description:
+		DCD = Data Carrier Detect
+		DTE is receiving a carrier from the DCE.
+		If the line state is detected, the LED is switched on.
+		If set to 0 (default), the LED will not evaluate CAR (DCD).
+		If set to 1, the LED will evaluate CAR (DCD).
+
+What:		/sys/class/leds/<led>/rng
+Date:		February 2024
+KernelVersion:	6.8
+Description:
+		RNG = Ring Indicator
+		DCE has detected an incoming ring signal on the telephone
+		line. If the line state is detected, the LED is switched on.
+		If set to 0 (default), the LED will not evaluate RNG.
+		If set to 1, the LED will evaluate RNG.

drivers/leds/trigger/ledtrig-tty.c

···
 	int rx, tx;
 	bool mode_rx;
 	bool mode_tx;
+	bool mode_cts;
+	bool mode_dsr;
+	bool mode_dcd;
+	bool mode_rng;
 };
 
 /* Indicates which state the LED should now display */
 enum led_trigger_tty_state {
 	TTY_LED_BLINK,
+	TTY_LED_ENABLE,
 	TTY_LED_DISABLE,
 };
 
 enum led_trigger_tty_modes {
 	TRIGGER_TTY_RX = 0,
 	TRIGGER_TTY_TX,
+	TRIGGER_TTY_CTS,
+	TRIGGER_TTY_DSR,
+	TRIGGER_TTY_DCD,
+	TRIGGER_TTY_RNG,
 };
 
 static int ledtrig_tty_wait_for_completion(struct device *dev)
···
 	case TRIGGER_TTY_TX:
 		state = trigger_data->mode_tx;
 		break;
+	case TRIGGER_TTY_CTS:
+		state = trigger_data->mode_cts;
+		break;
+	case TRIGGER_TTY_DSR:
+		state = trigger_data->mode_dsr;
+		break;
+	case TRIGGER_TTY_DCD:
+		state = trigger_data->mode_dcd;
+		break;
+	case TRIGGER_TTY_RNG:
+		state = trigger_data->mode_rng;
+		break;
 	}
 
 	return sysfs_emit(buf, "%u\n", state);
···
 	case TRIGGER_TTY_TX:
 		trigger_data->mode_tx = state;
 		break;
+	case TRIGGER_TTY_CTS:
+		trigger_data->mode_cts = state;
+		break;
+	case TRIGGER_TTY_DSR:
+		trigger_data->mode_dsr = state;
+		break;
+	case TRIGGER_TTY_DCD:
+		trigger_data->mode_dcd = state;
+		break;
+	case TRIGGER_TTY_RNG:
+		trigger_data->mode_rng = state;
+		break;
 	}
 
 	return size;
···
 
 DEFINE_TTY_TRIGGER(rx, TRIGGER_TTY_RX);
 DEFINE_TTY_TRIGGER(tx, TRIGGER_TTY_TX);
+DEFINE_TTY_TRIGGER(cts, TRIGGER_TTY_CTS);
+DEFINE_TTY_TRIGGER(dsr, TRIGGER_TTY_DSR);
+DEFINE_TTY_TRIGGER(dcd, TRIGGER_TTY_DCD);
+DEFINE_TTY_TRIGGER(rng, TRIGGER_TTY_RNG);
 
 static void ledtrig_tty_work(struct work_struct *work)
 {
···
 		container_of(work, struct ledtrig_tty_data, dwork.work);
 	enum led_trigger_tty_state state = TTY_LED_DISABLE;
 	unsigned long interval = LEDTRIG_TTY_INTERVAL;
+	bool invert = false;
+	int status;
 	int ret;
 
 	if (!trigger_data->ttyname)
···
 		trigger_data->tty = tty;
 	}
 
+	status = tty_get_tiocm(trigger_data->tty);
+	if (status > 0) {
+		if (trigger_data->mode_cts) {
+			if (status & TIOCM_CTS)
+				state = TTY_LED_ENABLE;
+		}
+
+		if (trigger_data->mode_dsr) {
+			if (status & TIOCM_DSR)
+				state = TTY_LED_ENABLE;
+		}
+
+		if (trigger_data->mode_dcd) {
+			if (status & TIOCM_CAR)
+				state = TTY_LED_ENABLE;
+		}
+
+		if (trigger_data->mode_rng) {
+			if (status & TIOCM_RNG)
+				state = TTY_LED_ENABLE;
+		}
+	}
+
+	/*
+	 * The evaluation of rx/tx must be done after the evaluation
+	 * of TIOCM_*, because rx/tx has priority.
+	 */
 	if (trigger_data->mode_rx || trigger_data->mode_tx) {
 		struct serial_icounter_struct icount;
 
···
 
 		if (trigger_data->mode_tx && (icount.tx != trigger_data->tx)) {
 			trigger_data->tx = icount.tx;
+			invert = state == TTY_LED_ENABLE;
 			state = TTY_LED_BLINK;
 		}
 
 		if (trigger_data->mode_rx && (icount.rx != trigger_data->rx)) {
 			trigger_data->rx = icount.rx;
+			invert = state == TTY_LED_ENABLE;
 			state = TTY_LED_BLINK;
 		}
 	}
···
 	switch (state) {
 	case TTY_LED_BLINK:
 		led_blink_set_oneshot(trigger_data->led_cdev, &interval,
-				&interval, 0);
+				&interval, invert);
+		break;
+	case TTY_LED_ENABLE:
+		led_set_brightness(trigger_data->led_cdev,
+				trigger_data->led_cdev->blink_brightness);
 		break;
 	case TTY_LED_DISABLE:
 		fallthrough;
···
 	&dev_attr_ttyname.attr,
 	&dev_attr_rx.attr,
 	&dev_attr_tx.attr,
+	&dev_attr_cts.attr,
+	&dev_attr_dsr.attr,
+	&dev_attr_dcd.attr,
+	&dev_attr_rng.attr,
 	NULL
 };
 ATTRIBUTE_GROUPS(ledtrig_tty);