thermal: introduce clock cooling device

This patch introduces a new thermal cooling device based on common clock
framework. The original motivation to write this cooling device is to be
able to cool down thermal zones using clocks that feed co-processors, such
as GPUs, DSPs, Image Processing Co-processors, etc. But it is written
in a way that it can be used on top of any clock.

The implementation is pretty straight forward. The code creates
a thermal cooling device based on a pair of a struct device and a clock name.
The struct device is assumed to be usable by the OPP layer. The OPP layer
is used as source of the list of possible frequencies. The (cpufreq) frequency
table is then used as a map from frequencies to cooling states. Cooling
states are indexes to the frequency table.

The logic sits on top of common clock framework, specifically on clock
pre notifications. Any PRE_RATE_CHANGE is hijacked, and the transition is
only allowed when the new rate is within the thermal limit (cooling state -> freq).

When a thermal cooling device state transition is requested, the clock
is also checked to verify if the current clock rate is within the new
thermal limit.

Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Mike Turquette <mturquette@linaro.org>
Cc: Nishanth Menon <nm@ti.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Len Brown <len.brown@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-pm@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>

drivers/thermal/Kconfig

@@ -112,6 +112,18 @@ config CPU_THERMAL
 
 	  If you want this support, you should say Y here.
 
+config CLOCK_THERMAL
+	bool "Generic clock cooling support"
+	depends on COMMON_CLK
+	depends on PM_OPP
+	help
+	  This entry implements the generic clock cooling mechanism through
+	  frequency clipping. Typically used to cool off co-processors. The
+	  device that is configured to use this cooling mechanism will be
+	  controlled to reduce clock frequency whenever temperature is high.
+
+	  If you want this support, you should say Y here.
+
 config THERMAL_EMULATION
 	bool "Thermal emulation mode support"
 	help

drivers/thermal/Makefile

@@ -18,6 +18,9 @@ thermal_sys-$(CONFIG_THERMAL_GOV_USER_SPACE)	+= user_space.o
 # cpufreq cooling
 thermal_sys-$(CONFIG_CPU_THERMAL)	+= cpu_cooling.o
 
+# clock cooling
+thermal_sys-$(CONFIG_CLOCK_THERMAL)	+= clock_cooling.o
+
 # platform thermal drivers
 obj-$(CONFIG_SPEAR_THERMAL)	+= spear_thermal.o
 obj-$(CONFIG_RCAR_THERMAL)	+= rcar_thermal.o

include/linux/clock_cooling.h

+/*
+ *  linux/include/linux/clock_cooling.h
+ *
+ *  Copyright (C) 2014 Eduardo Valentin <edubezval@gmail.com>
+ *
+ *  Copyright (C) 2013	Texas Instruments Inc.
+ *  Contact:  Eduardo Valentin <eduardo.valentin@ti.com>
+ *
+ *  Highly based on cpu_cooling.c.
+ *  Copyright (C) 2012	Samsung Electronics Co., Ltd(http://www.samsung.com)
+ *  Copyright (C) 2012  Amit Daniel <amit.kachhap@linaro.org>
+ *
+ *  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 of the License.
+ *
+ *  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.
+ */
+
+#ifndef __CPU_COOLING_H__
+#define __CPU_COOLING_H__
+
+#include <linux/of.h>
+#include <linux/thermal.h>
+#include <linux/cpumask.h>
+
+#ifdef CONFIG_CLOCK_THERMAL
+/**
+ * clock_cooling_register - function to create clock cooling device.
+ * @dev: struct device pointer to the device used as clock cooling device.
+ * @clock_name: string containing the clock used as cooling mechanism.
+ */
+struct thermal_cooling_device *
+clock_cooling_register(struct device *dev, const char *clock_name);
+
+/**
+ * clock_cooling_unregister - function to remove clock cooling device.
+ * @cdev: thermal cooling device pointer.
+ */
+void clock_cooling_unregister(struct thermal_cooling_device *cdev);
+
+unsigned long clock_cooling_get_level(struct thermal_cooling_device *cdev,
+				      unsigned long freq);
+#else /* !CONFIG_CLOCK_THERMAL */
+static inline struct thermal_cooling_device *
+clock_cooling_register(struct device *dev, const char *clock_name)
+{
+	return NULL;
+}
+static inline
+void clock_cooling_unregister(struct thermal_cooling_device *cdev)
+{
+}
+static inline
+unsigned long clock_cooling_get_level(struct thermal_cooling_device *cdev,
+				      unsigned long freq)
+{
+	return THERMAL_CSTATE_INVALID;
+}
+#endif	/* CONFIG_CLOCK_THERMAL */
+
+#endif /* __CPU_COOLING_H__ */