thermal: core: Add user thresholds support

The user thresholds mechanism is a way to have the userspace to tell
the thermal framework to send a notification when a temperature limit
is crossed. There is no id, no hysteresis, just the temperature and
the direction of the limit crossing. That means we can be notified
when a threshold is crossed the way up only, or the way down only or
both ways. That allows to create hysteresis values if it is needed.

A threshold can be added, deleted or flushed. The latter means all
thresholds belonging to a thermal zone will be deleted.

When a threshold is added:

 - if the same threshold (temperature and direction) exists, an error
   is returned

 - if a threshold is specified with the same temperature but a
   different direction, the specified direction is added

 - if there is no threshold with the same temperature then it is
   created

When a threshold is deleted:

 - if the same threshold (temperature and direction) exists, it is
   deleted

 - if a threshold is specified with the same temperature but a
   different direction, the specified direction is removed

 - if there is no threshold with the same temperature, then an error
   is returned

When the threshold are flushed:

 - All thresholds related to a thermal zone are deleted

When a threshold is crossed:

 - the userspace does not need to know which threshold(s) have been
   crossed, it will be notified with the current temperature and the
   previous temperature

 - if multiple thresholds have been crossed between two updates only
   one notification will be send to the userspace, it is pointless to
   send a notification per thresholds crossed as the userspace can
   handle that easily when it has the temperature delta information

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://patch.msgid.link/20240923100005.2532430-2-daniel.lezcano@linaro.org
[ rjw: Subject edit, use BIT(0) and BIT(1) in symbol definitions ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/thermal/Makefile

@@ -6,6 +6,7 @@ CFLAGS_thermal_core.o		:= -I$(src)
 obj-$(CONFIG_THERMAL)		+= thermal_sys.o
 thermal_sys-y			+= thermal_core.o thermal_sysfs.o
 thermal_sys-y			+= thermal_trip.o thermal_helpers.o
+thermal_sys-y			+= thermal_thresholds.o
 
 # netlink interface to manage the thermal framework
 thermal_sys-$(CONFIG_THERMAL_NETLINK)		+= thermal_netlink.o

drivers/thermal/thermal_core.h

@@ -13,6 +13,7 @@
 #include <linux/thermal.h>
 
 #include "thermal_netlink.h"
+#include "thermal_thresholds.h"
 #include "thermal_debugfs.h"
 
 struct thermal_attr {
@@ -139,6 +140,7 @@ struct thermal_zone_device {
 #ifdef CONFIG_THERMAL_DEBUGFS
 	struct thermal_debugfs *debugfs;
 #endif
+	struct list_head user_thresholds;
 	struct thermal_trip_desc trips[] __counted_by(num_trips);
 };
 

drivers/thermal/thermal_thresholds.c

@@ -0,0 +1,229 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright 2024 Linaro Limited
+ *
+ * Author: Daniel Lezcano <daniel.lezcano@linaro.org>
+ *
+ * Thermal thresholds
+ */
+#include <linux/list.h>
+#include <linux/list_sort.h>
+#include <linux/slab.h>
+
+#include "thermal_core.h"
+#include "thermal_thresholds.h"
+
+int thermal_thresholds_init(struct thermal_zone_device *tz)
+{
+	INIT_LIST_HEAD(&tz->user_thresholds);
+
+	return 0;
+}
+
+void thermal_thresholds_flush(struct thermal_zone_device *tz)
+{
+	struct list_head *thresholds = &tz->user_thresholds;
+	struct user_threshold *entry, *tmp;
+
+	lockdep_assert_held(&tz->lock);
+
+	list_for_each_entry_safe(entry, tmp, thresholds, list_node) {
+		list_del(&entry->list_node);
+		kfree(entry);
+	}
+
+	__thermal_zone_device_update(tz, THERMAL_TZ_FLUSH_THRESHOLDS);
+}
+
+void thermal_thresholds_exit(struct thermal_zone_device *tz)
+{
+	thermal_thresholds_flush(tz);
+}
+
+static int __thermal_thresholds_cmp(void *data,
+				    const struct list_head *l1,
+				    const struct list_head *l2)
+{
+	struct user_threshold *t1 = container_of(l1, struct user_threshold, list_node);
+	struct user_threshold *t2 = container_of(l2, struct user_threshold, list_node);
+
+	return t1->temperature - t2->temperature;
+}
+
+static struct user_threshold *__thermal_thresholds_find(const struct list_head *thresholds,
+							int temperature)
+{
+	struct user_threshold *t;
+
+	list_for_each_entry(t, thresholds, list_node)
+		if (t->temperature == temperature)
+			return t;
+
+	return NULL;
+}
+
+static bool __thermal_threshold_is_crossed(struct user_threshold *threshold, int temperature,
+					   int last_temperature, int direction,
+					   int *low, int *high)
+{
+
+	if (temperature >= threshold->temperature) {
+		if (threshold->temperature > *low &&
+		    THERMAL_THRESHOLD_WAY_DOWN & threshold->direction)
+			*low = threshold->temperature;
+
+		if (last_temperature < threshold->temperature &&
+		    threshold->direction & direction)
+			return true;
+	} else {
+		if (threshold->temperature < *high && THERMAL_THRESHOLD_WAY_UP
+		    & threshold->direction)
+			*high = threshold->temperature;
+
+		if (last_temperature >= threshold->temperature &&
+		    threshold->direction & direction)
+			return true;
+	}
+
+	return false;
+}
+
+static bool thermal_thresholds_handle_raising(struct list_head *thresholds, int temperature,
+					      int last_temperature, int *low, int *high)
+{
+	struct user_threshold *t;
+
+	list_for_each_entry(t, thresholds, list_node) {
+		if (__thermal_threshold_is_crossed(t, temperature, last_temperature,
+						   THERMAL_THRESHOLD_WAY_UP, low, high))
+			return true;
+	}
+
+	return false;
+}
+
+static bool thermal_thresholds_handle_dropping(struct list_head *thresholds, int temperature,
+					       int last_temperature, int *low, int *high)
+{
+	struct user_threshold *t;
+
+	list_for_each_entry_reverse(t, thresholds, list_node) {
+		if (__thermal_threshold_is_crossed(t, temperature, last_temperature,
+						   THERMAL_THRESHOLD_WAY_DOWN, low, high))
+			return true;
+	}
+
+	return false;
+}
+
+void thermal_thresholds_handle(struct thermal_zone_device *tz, int *low, int *high)
+{
+	struct list_head *thresholds = &tz->user_thresholds;
+
+	int temperature = tz->temperature;
+	int last_temperature = tz->last_temperature;
+	bool notify;
+
+	lockdep_assert_held(&tz->lock);
+
+	/*
+	 * We need a second update in order to detect a threshold being crossed
+	 */
+	if (last_temperature == THERMAL_TEMP_INVALID)
+		return;
+
+	/*
+	 * The temperature is stable, so obviously we can not have
+	 * crossed a threshold.
+	 */
+	if (last_temperature == temperature)
+		return;
+
+	/*
+	 * Since last update the temperature:
+	 * - increased : thresholds are crossed the way up
+	 * - decreased : thresholds are crossed the way down
+	 */
+	if (temperature > last_temperature)
+		notify = thermal_thresholds_handle_raising(thresholds, temperature,
+							   last_temperature, low, high);
+	else
+		notify = thermal_thresholds_handle_dropping(thresholds, temperature,
+							    last_temperature, low, high);
+
+	if (notify)
+		pr_debug("A threshold has been crossed the way %s, with a temperature=%d, last_temperature=%d\n",
+			 temperature > last_temperature ? "up" : "down", temperature, last_temperature);
+}
+
+int thermal_thresholds_add(struct thermal_zone_device *tz, int temperature, int direction)
+{
+	struct list_head *thresholds = &tz->user_thresholds;
+	struct user_threshold *t;
+
+	lockdep_assert_held(&tz->lock);
+
+	t = __thermal_thresholds_find(thresholds, temperature);
+	if (t) {
+		if (t->direction == direction)
+			return -EEXIST;
+
+		t->direction |= direction;
+	} else {
+
+		t = kmalloc(sizeof(*t), GFP_KERNEL);
+		if (!t)
+			return -ENOMEM;
+
+		INIT_LIST_HEAD(&t->list_node);
+		t->temperature = temperature;
+		t->direction = direction;
+		list_add(&t->list_node, thresholds);
+		list_sort(NULL, thresholds, __thermal_thresholds_cmp);
+	}
+
+	__thermal_zone_device_update(tz, THERMAL_TZ_ADD_THRESHOLD);
+
+	return 0;
+}
+
+int thermal_thresholds_delete(struct thermal_zone_device *tz, int temperature, int direction)
+{
+	struct list_head *thresholds = &tz->user_thresholds;
+	struct user_threshold *t;
+
+	lockdep_assert_held(&tz->lock);
+
+	t = __thermal_thresholds_find(thresholds, temperature);
+	if (!t)
+		return -ENOENT;
+
+	if (t->direction == direction) {
+		list_del(&t->list_node);
+		kfree(t);
+	} else {
+		t->direction &= ~direction;
+	}
+
+	__thermal_zone_device_update(tz, THERMAL_TZ_DEL_THRESHOLD);
+
+	return 0;
+}
+
+int thermal_thresholds_for_each(struct thermal_zone_device *tz,
+				int (*cb)(struct user_threshold *, void *arg), void *arg)
+{
+	struct list_head *thresholds = &tz->user_thresholds;
+	struct user_threshold *entry;
+	int ret;
+
+	lockdep_assert_held(&tz->lock);
+
+	list_for_each_entry(entry, thresholds, list_node) {
+		ret = cb(entry, arg);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}

drivers/thermal/thermal_thresholds.h

@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __THERMAL_THRESHOLDS_H__
+#define __THERMAL_THRESHOLDS_H__
+
+struct user_threshold {
+	struct list_head list_node;
+	int temperature;
+	int direction;
+};
+
+int thermal_thresholds_init(struct thermal_zone_device *tz);
+void thermal_thresholds_exit(struct thermal_zone_device *tz);
+void thermal_thresholds_flush(struct thermal_zone_device *tz);
+void thermal_thresholds_handle(struct thermal_zone_device *tz, int *low, int *high);
+int thermal_thresholds_add(struct thermal_zone_device *tz, int temperature, int direction);
+int thermal_thresholds_delete(struct thermal_zone_device *tz, int temperature, int direction);
+int thermal_thresholds_for_each(struct thermal_zone_device *tz,
+				int (*cb)(struct user_threshold *, void *arg), void *arg);
+#endif

include/linux/thermal.h

@@ -56,6 +56,9 @@ enum thermal_notify_event {
 	THERMAL_TZ_UNBIND_CDEV, /* Cooling dev is unbind from the thermal zone */
 	THERMAL_INSTANCE_WEIGHT_CHANGED, /* Thermal instance weight changed */
 	THERMAL_TZ_RESUME, /* Thermal zone is resuming after system sleep */
+	THERMAL_TZ_ADD_THRESHOLD, /* Threshold added */
+	THERMAL_TZ_DEL_THRESHOLD, /* Threshold deleted */
+	THERMAL_TZ_FLUSH_THRESHOLDS, /* All thresholds deleted */
 };
 
 /**

include/uapi/linux/thermal.h

@@ -3,6 +3,8 @@
 #define _UAPI_LINUX_THERMAL_H
 
 #define THERMAL_NAME_LENGTH	20
+#define THERMAL_THRESHOLD_WAY_UP	BIT(0)
+#define THERMAL_THRESHOLD_WAY_DOWN	BIT(1)
 
 enum thermal_device_mode {
 	THERMAL_DEVICE_DISABLED = 0,