[v3,1/1] leds: trigger: Add new LED Input events trigger

diff --git a/drivers/leds/trigger/Kconfig b/drivers/leds/trigger/Kconfig
index 31576952e181..c11282a74b5a 100644
--- a/drivers/leds/trigger/Kconfig
+++ b/drivers/leds/trigger/Kconfig
@@ -145,4 +145,20 @@  config LEDS_TRIGGER_TTY
 
 	  When build as a module this driver will be called ledtrig-tty.
 
+config LEDS_TRIGGER_INPUT_EVENTS
+	tristate "LED Input events trigger"
+	depends on INPUT
+	help
+	  Turn LEDs on when there is input (/dev/input/event*) activity and turn
+	  them back off again after there has been no activity for 5 seconds.
+
+	  This is primarily intended to control LEDs which are a backlight for
+	  capacitive touch-buttons, such as e.g. the menu / home / back buttons
+	  found on the bottom bezel of many older smartphones and tablets.
+
+	  This can also be used to turn on the keyboard backlight LED on
+	  input events and turn the keyboard backlight off again when idle.
+
+	  When build as a module this driver will be called ledtrig-input-events.
+
 endif # LEDS_TRIGGERS
diff --git a/drivers/leds/trigger/Makefile b/drivers/leds/trigger/Makefile
index 242f6c4e3453..3b3628889f68 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_TTY)		+= ledtrig-tty.o
+obj-$(CONFIG_LEDS_TRIGGER_INPUT_EVENTS)	+= ledtrig-input-events.o
diff --git a/drivers/leds/trigger/ledtrig-input-events.c b/drivers/leds/trigger/ledtrig-input-events.c
new file mode 100644
index 000000000000..1de0176799f9
--- /dev/null
+++ b/drivers/leds/trigger/ledtrig-input-events.c
@@ -0,0 +1,233 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Input Events LED trigger
+ *
+ * Copyright (C) 2024 Hans de Goede <hansg@kernel.org>
+ * Partially based on Atsushi Nemoto's ledtrig-heartbeat.c.
+ */
+
+#include <linux/input.h>
+#include <linux/jiffies.h>
+#include <linux/leds.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/workqueue.h>
+#include "../leds.h"
+
+#define DEFAULT_LED_OFF_DELAY_MS			5000
+
+struct input_events_data {
+	struct input_handler handler;
+	struct delayed_work work;
+	spinlock_t lock;
+	struct led_classdev *led_cdev;
+	int led_cdev_saved_flags;
+	/* To avoid repeatedly setting the brightness while there are events */
+	bool led_on;
+	unsigned long led_off_time;
+	unsigned long led_off_delay;
+};
+
+static void led_input_events_work(struct work_struct *work)
+{
+	struct input_events_data *data =
+		container_of(work, struct input_events_data, work.work);
+
+	spin_lock_irq(&data->lock);
+
+	/*
+	 * This time_after_eq() check avoids a race where this work starts
+	 * running before a new event pushed led_off_time back.
+	 */
+	if (time_after_eq(jiffies, data->led_off_time)) {
+		led_set_brightness_nosleep(data->led_cdev, LED_OFF);
+		data->led_on = false;
+	}
+
+	spin_unlock_irq(&data->lock);
+}
+
+static ssize_t delay_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct input_events_data *input_events_data = led_trigger_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%lu\n", input_events_data->led_off_delay);
+}
+
+static ssize_t delay_store(struct device *dev, struct device_attribute *attr,
+			   const char *buf, size_t size)
+{
+	struct input_events_data *input_events_data = led_trigger_get_drvdata(dev);
+	unsigned long delay;
+	int ret;
+
+	ret = kstrtoul(buf, 0, &delay);
+	if (ret)
+		return ret;
+
+	/* Clamp between 0.5 and 1000 seconds */
+	delay = clamp_val(delay, 500UL, 1000000UL);
+	input_events_data->led_off_delay = msecs_to_jiffies(delay);
+
+	return size;
+}
+
+static DEVICE_ATTR_RW(delay);
+
+static struct attribute *input_events_led_attrs[] = {
+	&dev_attr_delay.attr,
+	NULL
+};
+ATTRIBUTE_GROUPS(input_events_led);
+
+static void input_events_event(struct input_handle *handle, unsigned int type,
+			       unsigned int code, int val)
+{
+	struct input_events_data *data =
+		container_of(handle->handler, struct input_events_data, handler);
+	unsigned long led_off_delay = READ_ONCE(data->led_off_delay);
+	struct led_classdev *led_cdev = data->led_cdev;
+	unsigned long flags;
+
+	if (test_and_clear_bit(LED_BLINK_BRIGHTNESS_CHANGE, &led_cdev->work_flags))
+		led_cdev->blink_brightness = led_cdev->new_blink_brightness;
+
+	spin_lock_irqsave(&data->lock, flags);
+
+	if (!data->led_on) {
+		led_set_brightness_nosleep(led_cdev, led_cdev->blink_brightness);
+		data->led_on = true;
+	}
+	data->led_off_time = jiffies + led_off_delay;
+
+	spin_unlock_irqrestore(&data->lock, flags);
+
+	mod_delayed_work(system_wq, &data->work, led_off_delay);
+}
+
+static int input_events_connect(struct input_handler *handler, struct input_dev *dev,
+				const struct input_device_id *id)
+{
+	struct input_handle *handle;
+	int ret;
+
+	handle = kzalloc(sizeof(*handle), GFP_KERNEL);
+	if (!handle)
+		return -ENOMEM;
+
+	handle->dev = dev;
+	handle->handler = handler;
+	handle->name = "input-events";
+
+	ret = input_register_handle(handle);
+	if (ret)
+		goto err_free_handle;
+
+	ret = input_open_device(handle);
+	if (ret)
+		goto err_unregister_handle;
+
+	return 0;
+
+err_unregister_handle:
+	input_unregister_handle(handle);
+err_free_handle:
+	kfree(handle);
+	return ret;
+}
+
+static void input_events_disconnect(struct input_handle *handle)
+{
+	input_close_device(handle);
+	input_unregister_handle(handle);
+	kfree(handle);
+}
+
+static const struct input_device_id input_events_ids[] = {
+	{
+		.flags = INPUT_DEVICE_ID_MATCH_EVBIT,
+		.evbit = { BIT_MASK(EV_KEY) },
+	},
+	{
+		.flags = INPUT_DEVICE_ID_MATCH_EVBIT,
+		.evbit = { BIT_MASK(EV_REL) },
+	},
+	{
+		.flags = INPUT_DEVICE_ID_MATCH_EVBIT,
+		.evbit = { BIT_MASK(EV_ABS) },
+	},
+	{ }
+};
+
+static int input_events_activate(struct led_classdev *led_cdev)
+{
+	struct input_events_data *data;
+	int ret;
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->handler.name = "input-events";
+	data->handler.event = input_events_event;
+	data->handler.connect = input_events_connect;
+	data->handler.disconnect = input_events_disconnect;
+	data->handler.id_table = input_events_ids;
+
+	INIT_DELAYED_WORK(&data->work, led_input_events_work);
+	spin_lock_init(&data->lock);
+
+	data->led_cdev = led_cdev;
+	data->led_cdev_saved_flags = led_cdev->flags;
+	data->led_off_delay = msecs_to_jiffies(DEFAULT_LED_OFF_DELAY_MS);
+
+	/*
+	 * Use led_cdev->blink_brightness + LED_BLINK_SW flag so that sysfs
+	 * brightness writes will change led_cdev->new_blink_brightness for
+	 * configuring the on state brightness (like ledtrig-heartbeat).
+	 */
+	if (!led_cdev->blink_brightness)
+		led_cdev->blink_brightness = led_cdev->max_brightness;
+
+	/* Start with LED off */
+	led_set_brightness_nosleep(data->led_cdev, LED_OFF);
+
+	ret = input_register_handler(&data->handler);
+	if (ret) {
+		kfree(data);
+		return ret;
+	}
+
+	set_bit(LED_BLINK_SW, &led_cdev->work_flags);
+
+	/* Turn LED off during suspend, original flags are restored on deactivate() */
+	led_cdev->flags |= LED_CORE_SUSPENDRESUME;
+
+	led_set_trigger_data(led_cdev, data);
+	return 0;
+}
+
+static void input_events_deactivate(struct led_classdev *led_cdev)
+{
+	struct input_events_data *data = led_get_trigger_data(led_cdev);
+
+	led_cdev->flags = data->led_cdev_saved_flags;
+	clear_bit(LED_BLINK_SW, &led_cdev->work_flags);
+	input_unregister_handler(&data->handler);
+	cancel_delayed_work_sync(&data->work);
+	kfree(data);
+}
+
+static struct led_trigger input_events_led_trigger = {
+	.name       = "input-events",
+	.activate   = input_events_activate,
+	.deactivate = input_events_deactivate,
+	.groups     = input_events_led_groups,
+};
+module_led_trigger(input_events_led_trigger);
+
+MODULE_AUTHOR("Hans de Goede <hansg@kernel.org>");
+MODULE_DESCRIPTION("Input Events LED trigger");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("ledtrig:input-events");