leds: Add the actpwr trigger

The actpwr trigger is a meta trigger that cycles between an inverted
mmc0 and default-on. It is written in a way that could fairly easily
be generalised to support alternative sets of source triggers.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>

drivers/leds/trigger/Kconfig

@@ -168,4 +168,15 @@ config LEDS_TRIGGER_INPUT_EVENTS
 
 	  When build as a module this driver will be called ledtrig-input-events.
 
+config LEDS_TRIGGER_ACTPWR
+	tristate "ACT/PWR Input Trigger"
+	depends on LEDS_TRIGGERS
+	help
+	  This trigger is intended for platforms that have one software-
+	  controllable LED and no dedicated activity or power LEDs, hence the
+	  need to make the one LED perform both functions. It cycles between
+	  default-on and an inverted mmc0 every 500ms, guaranteeing that it is
+	  on for at least half of the time.
+	  If unsure, say N.
+
 endif # LEDS_TRIGGERS

drivers/leds/trigger/Makefile

@@ -17,3 +17,4 @@ 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
+obj-$(CONFIG_LEDS_TRIGGER_ACTPWR)	+= ledtrig-actpwr.o

drivers/leds/trigger/ledtrig-actpwr.c

@@ -0,0 +1,190 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Activity/power trigger
+ *
+ * Copyright (C) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * Based on Atsushi Nemoto's ledtrig-heartbeat.c, although there may be
+ * nothing left of the original now.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/timer.h>
+#include <linux/leds.h>
+#include "../leds.h"
+
+enum {
+	TRIG_ACT,
+	TRIG_PWR,
+
+	TRIG_COUNT
+};
+
+struct actpwr_trig_src {
+	const char *name;
+	int interval;
+	bool invert;
+};
+
+struct actpwr_vled {
+	struct led_classdev cdev;
+	struct actpwr_trig_data *parent;
+	enum led_brightness value;
+	unsigned int interval;
+	bool invert;
+};
+
+struct actpwr_trig_data {
+	struct led_trigger trig;
+	struct actpwr_vled virt_leds[TRIG_COUNT];
+	struct actpwr_vled *active;
+	struct timer_list timer;
+	int next_active;
+};
+
+static int actpwr_trig_activate(struct led_classdev *led_cdev);
+static void actpwr_trig_deactivate(struct led_classdev *led_cdev);
+
+static const struct actpwr_trig_src actpwr_trig_sources[TRIG_COUNT] = {
+	[TRIG_ACT] = { "mmc0", 500, true },
+	[TRIG_PWR] = { "default-on", 500, false },
+};
+
+static struct actpwr_trig_data actpwr_data = {
+	{
+		.name     = "actpwr",
+		.activate = actpwr_trig_activate,
+		.deactivate = actpwr_trig_deactivate,
+	}
+};
+
+static void actpwr_brightness_set(struct led_classdev *led_cdev,
+				  enum led_brightness value)
+{
+	struct actpwr_vled *vled = container_of(led_cdev, struct actpwr_vled,
+					       cdev);
+	struct actpwr_trig_data *trig = vled->parent;
+
+	if (vled->invert)
+		value = !value;
+	vled->value = value;
+
+	if (vled == trig->active)
+		led_trigger_event(&trig->trig, value);
+}
+
+static int actpwr_brightness_set_blocking(struct led_classdev *led_cdev,
+					  enum led_brightness value)
+{
+	actpwr_brightness_set(led_cdev, value);
+	return 0;
+}
+
+static enum led_brightness actpwr_brightness_get(struct led_classdev *led_cdev)
+{
+	struct actpwr_vled *vled = container_of(led_cdev, struct actpwr_vled,
+					      cdev);
+
+	return vled->value;
+}
+
+static void actpwr_trig_cycle(struct timer_list *t)
+{
+	struct actpwr_trig_data *trig  = &actpwr_data;
+	struct actpwr_vled *active;
+
+	active = &trig->virt_leds[trig->next_active];
+	trig->active = active;
+	trig->next_active = (trig->next_active + 1) % TRIG_COUNT;
+
+	led_trigger_event(&trig->trig, active->value);
+
+	mod_timer(&trig->timer, jiffies + msecs_to_jiffies(active->interval));
+}
+
+static int actpwr_trig_activate(struct led_classdev *led_cdev)
+{
+	struct actpwr_trig_data *trig  = &actpwr_data;
+
+	/* Start the timer if this is the first LED */
+	if (!trig->active)
+		actpwr_trig_cycle(&trig->timer);
+	else
+		led_set_brightness_nosleep(led_cdev, trig->active->value);
+
+	return 0;
+}
+
+static void actpwr_trig_deactivate(struct led_classdev *led_cdev)
+{
+	struct actpwr_trig_data *trig  = &actpwr_data;
+
+	if (list_empty(&trig->trig.led_cdevs)) {
+		timer_delete_sync(&trig->timer);
+		trig->active = NULL;
+	}
+}
+
+static int __init actpwr_trig_init(void)
+{
+	struct actpwr_trig_data *trig  = &actpwr_data;
+	int ret = 0;
+	int i;
+
+	timer_setup(&trig->timer, actpwr_trig_cycle, 0);
+
+	/* Register one "LED" for each source trigger */
+	for (i = 0; i < TRIG_COUNT; i++)
+	{
+		struct actpwr_vled *vled = &trig->virt_leds[i];
+		struct led_classdev *cdev = &vled->cdev;
+		const struct actpwr_trig_src *src = &actpwr_trig_sources[i];
+
+		vled->parent = trig;
+		vled->interval = src->interval;
+		vled->invert = src->invert;
+		cdev->name = src->name;
+		cdev->brightness_set = actpwr_brightness_set;
+		cdev->brightness_set_blocking = actpwr_brightness_set_blocking;
+		cdev->brightness_get = actpwr_brightness_get;
+		cdev->default_trigger = src->name;
+		ret = led_classdev_register(NULL, cdev);
+		if (ret)
+			goto error_classdev;
+	}
+
+	ret = led_trigger_register(&trig->trig);
+	if (ret)
+		goto error_classdev;
+
+	return 0;
+
+error_classdev:
+	while (i > 0)
+	{
+		i--;
+		led_classdev_unregister(&trig->virt_leds[i].cdev);
+	}
+
+	return ret;
+}
+
+static void __exit actpwr_trig_exit(void)
+{
+	int i;
+
+	led_trigger_unregister(&actpwr_data.trig);
+	for (i = 0; i < TRIG_COUNT; i++)
+	{
+		led_classdev_unregister(&actpwr_data.virt_leds[i].cdev);
+	}
+}
+
+module_init(actpwr_trig_init);
+module_exit(actpwr_trig_exit);
+
+MODULE_AUTHOR("Phil Elwell <phil@raspberrypi.com>");
+MODULE_DESCRIPTION("ACT/PWR LED trigger");
+MODULE_LICENSE("GPL v2");