[PATCH v3 3/6] thermal: Added Bang-bang thermal governor

Peter Feuerer
2014-05-03T18:01:59Z

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 <akpm@linux-foundation.org>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Andreas Mohr <andi@lisas.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Javi Merino <javi.merino@arm.com>
Signed-off-by: Peter Feuerer <peter@piie.net>
---
drivers/thermal/Kconfig | 10 +++
drivers/thermal/Makefile | 1 +
drivers/thermal/gov_bang_bang.c | 131 ++++++++++++++++++++++++++++++++++++++++
drivers/thermal/thermal_core.c | 5 ++
drivers/thermal/thermal_core.h | 8 +++
5 files changed, 155 insertions(+)
create mode 100644 drivers/thermal/gov_bang_bang.c

diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
index 2d51912..2ede94f 100644
--- a/drivers/thermal/Kconfig
+++ b/drivers/thermal/Kconfig
@@ -84,6 +84,16 @@ config THERMAL_GOV_STEP_WISE
Enable this to manage platform thermals using a simple linear
governor.

+config THERMAL_GOV_BANG_BANG
+ bool "Bang Bang thermal governor"
+ default y
+ 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
diff --git a/drivers/thermal/Makefile b/drivers/thermal/Makefile
index 54e4ec9..1c32a5d 100644
--- a/drivers/thermal/Makefile
+++ b/drivers/thermal/Makefile
@@ -11,6 +11,7 @@ thermal_sys-$(CONFIG_THERMAL_OF) += of-thermal.o

# 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

diff --git a/drivers/thermal/gov_bang_bang.c b/drivers/thermal/gov_bang_bang.c
new file mode 100644
index 0000000..228d0a6
--- /dev/null
+++ b/drivers/thermal/gov_bang_bang.c
@@ -0,0 +1,131 @@
+/*
+ * gov_bang_bang.c - A simple thermal throttling governor using hysteresis
+ *
+ * Copyright (C) 2014 Peter Feuerer <peter@piie.net>
+ *
+ * Based on step_wise.c with following Copyrights:
+ * Copyright (C) 2012 Intel Corp
+ * Copyright (C) 2012 Durgadoss R <durgadoss.r@intel.com>
+ *
+ *
+ * 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_throttle - 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_throttle(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_throttle,
+};
+
+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);
+}
diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
index 71b0ec0..4c2726b 100644
--- a/drivers/thermal/thermal_core.c
+++ b/drivers/thermal/thermal_core.c
@@ -1790,6 +1790,10 @@ static int __init thermal_register_governors(void)
if (result)
return result;

+ result = thermal_gov_bang_bang_register();
+ if (result)
+ return result;
+
return thermal_gov_user_space_register();
}

@@ -1797,6 +1801,7 @@ static void thermal_unregister_governors(void)
{
thermal_gov_step_wise_unregister();
thermal_gov_fair_share_unregister();
+ thermal_gov_bang_bang_unregister();
thermal_gov_user_space_unregister();
}

diff --git a/drivers/thermal/thermal_core.h b/drivers/thermal/thermal_core.h
index 3db339f..d15d243 100644
--- a/drivers/thermal/thermal_core.h
+++ b/drivers/thermal/thermal_core.h
@@ -69,6 +69,14 @@ static inline int thermal_gov_fair_share_register(void) { return 0; }
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);
--
1.9.2