thermal: Added Bang-bang thermal governor

The bang-bang thermal governor uses a hysteresis to switch abruptly on
or off a cooling device. It is intended to control fans, which can
not be throttled but just switched on or off.
Bang-bang cannot be set as default governor as it is intended for
special devices only. For those special devices the driver needs to
explicitely request it.

Cc: Andrew Morton <[e-mail]>
Cc: Zhang Rui <[e-mail]>
Cc: Andreas Mohr <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Javi Merino <[e-mail]>
Cc: [e-mail]
Signed-off-by: Peter Feuerer <[e-mail]>
Signed-off-by: Zhang Rui <[e-mail]>

drivers/thermal/Kconfig

···
 	  Enable this to manage platform thermals using a simple linear
 	  governor.
 
+config THERMAL_GOV_BANG_BANG
+	bool "Bang Bang thermal governor"
+	default n
+	help
+	  Enable this to manage platform thermals using bang bang governor.
+
+	  Say 'Y' here if you want to use two point temperature regulation
+	  used for fans without throttling.  Some fan drivers depend on this
+	  governor to be enabled (e.g. acerhdf).
+
 config THERMAL_GOV_USER_SPACE
 	bool "User_space thermal governor"
 	help

drivers/thermal/Makefile

···
 
 # governors
 thermal_sys-$(CONFIG_THERMAL_GOV_FAIR_SHARE)	+= fair_share.o
+thermal_sys-$(CONFIG_THERMAL_GOV_BANG_BANG)	+= gov_bang_bang.o
 thermal_sys-$(CONFIG_THERMAL_GOV_STEP_WISE)	+= step_wise.o
 thermal_sys-$(CONFIG_THERMAL_GOV_USER_SPACE)	+= user_space.o
 

drivers/thermal/gov_bang_bang.c

···
+/*
+ *  gov_bang_bang.c - A simple thermal throttling governor using hysteresis
+ *
+ *  Copyright (C) 2014 Peter Feuerer <[e-mail]>
+ *
+ *  Based on step_wise.c with following Copyrights:
+ *  Copyright (C) 2012 Intel Corp
+ *  Copyright (C) 2012 Durgadoss R <[e-mail]>
+ *
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 2.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
+ * the GNU General Public License for more details.
+ *
+ */
+
+#include <linux/thermal.h>
+
+#include "thermal_core.h"
+
+static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
+{
+	long trip_temp;
+	unsigned long trip_hyst;
+	struct thermal_instance *instance;
+
+	tz->ops->get_trip_temp(tz, trip, &trip_temp);
+	tz->ops->get_trip_hyst(tz, trip, &trip_hyst);
+
+	dev_dbg(&tz->device, "Trip%d[temp=%ld]:temp=%d:hyst=%ld\n",
+				trip, trip_temp, tz->temperature,
+				trip_hyst);
+
+	mutex_lock(&tz->lock);
+
+	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
+		if (instance->trip != trip)
+			continue;
+
+		/* in case fan is in initial state, switch the fan off */
+		if (instance->target == THERMAL_NO_TARGET)
+			instance->target = 0;
+
+		/* in case fan is neither on nor off set the fan to active */
+		if (instance->target != 0 && instance->target != 1) {
+			pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
+					instance->name, instance->target);
+			instance->target = 1;
+		}
+
+		/*
+		 * enable fan when temperature exceeds trip_temp and disable
+		 * the fan in case it falls below trip_temp minus hysteresis
+		 */
+		if (instance->target == 0 && tz->temperature >= trip_temp)
+			instance->target = 1;
+		else if (instance->target == 1 &&
+				tz->temperature < trip_temp - trip_hyst)
+			instance->target = 0;
+
+		dev_dbg(&instance->cdev->device, "target=%d\n",
+					(int)instance->target);
+
+		instance->cdev->updated = false; /* cdev needs update */
+	}
+
+	mutex_unlock(&tz->lock);
+}
+
+/**
+ * bang_bang_control - controls devices associated with the given zone
+ * @tz - thermal_zone_device
+ * @trip - the trip point
+ *
+ * Regulation Logic: a two point regulation, deliver cooling state depending
+ * on the previous state shown in this diagram:
+ *
+ *                Fan:   OFF    ON
+ *
+ *                              |
+ *                              |
+ *          trip_temp:    +---->+
+ *                        |     |        ^
+ *                        |     |        |
+ *                        |     |   Temperature
+ * (trip_temp - hyst):    +<----+
+ *                        |
+ *                        |
+ *                        |
+ *
+ *   * If the fan is not running and temperature exceeds trip_temp, the fan
+ *     gets turned on.
+ *   * In case the fan is running, temperature must fall below
+ *     (trip_temp - hyst) so that the fan gets turned off again.
+ *
+ */
+static int bang_bang_control(struct thermal_zone_device *tz, int trip)
+{
+	struct thermal_instance *instance;
+
+	thermal_zone_trip_update(tz, trip);
+
+	mutex_lock(&tz->lock);
+
+	list_for_each_entry(instance, &tz->thermal_instances, tz_node)
+		thermal_cdev_update(instance->cdev);
+
+	mutex_unlock(&tz->lock);
+
+	return 0;
+}
+
+static struct thermal_governor thermal_gov_bang_bang = {
+	.name		= "bang_bang",
+	.throttle	= bang_bang_control,
+};
+
+int thermal_gov_bang_bang_register(void)
+{
+	return thermal_register_governor(&thermal_gov_bang_bang);
+}
+
+void thermal_gov_bang_bang_unregister(void)
+{
+	thermal_unregister_governor(&thermal_gov_bang_bang);
+}

drivers/thermal/thermal_core.c

···
 	if (result)
 		return result;
 
+	result = thermal_gov_bang_bang_register();
+	if (result)
+		return result;
+
 	return thermal_gov_user_space_register();
 }
 
···
 {
 	thermal_gov_step_wise_unregister();
 	thermal_gov_fair_share_unregister();
+	thermal_gov_bang_bang_unregister();
 	thermal_gov_user_space_unregister();
 }
 

drivers/thermal/thermal_core.h

···
 static inline void thermal_gov_fair_share_unregister(void) {}
 #endif /* CONFIG_THERMAL_GOV_FAIR_SHARE */
 
+#ifdef CONFIG_THERMAL_GOV_BANG_BANG
+int thermal_gov_bang_bang_register(void);
+void thermal_gov_bang_bang_unregister(void);
+#else
+static inline int thermal_gov_bang_bang_register(void) { return 0; }
+static inline void thermal_gov_bang_bang_unregister(void) {}
+#endif /* CONFIG_THERMAL_GOV_BANG_BANG */
+
 #ifdef CONFIG_THERMAL_GOV_USER_SPACE
 int thermal_gov_user_space_register(void);
 void thermal_gov_user_space_unregister(void);