diff --git a/Documentation/thermal/intel_powerclamp.txt b/Documentation/thermal/intel_powerclamp.txt
new file mode 100644
index 0000000..332de4a
--- /dev/null
+++ b/Documentation/thermal/intel_powerclamp.txt
@@ -0,0 +1,307 @@
+			 =======================
+			 INTEL POWERCLAMP DRIVER
+			 =======================
+By: Arjan van de Ven <arjan@linux.intel.com>
+    Jacob Pan <jacob.jun.pan@linux.intel.com>
+
+Contents:
+	(*) Introduction
+	    - Goals and Objectives
+
+	(*) Theory of Operation
+	    - Idle Injection
+	    - Calibration
+
+	(*) Performance Analysis
+	    - Effectiveness and Limitations
+	    - Power vs Performance
+	    - Scalability
+	    - Calibration
+	    - Comparison with Alternative Techniques
+
+	(*) Usage and Interfaces
+	    - Generic Thermal Layer (sysfs)
+	    - Kernel APIs (TBD)
+
+============
+INTRODUCTION
+============
+
+Consider the situation where a system’s power consumption must be
+reduced at runtime, due to power budget, thermal constraint, or noise
+level, and where active cooling is not preferred. Software managed
+passive power reduction must be performed to prevent the hardware
+actions that are designed for catastrophic scenarios.
+
+Currently, P-states, T-states (clock modulation), and CPU offlining
+are used for CPU throttling.
+
+On Intel CPUs, C-states provide effective power reduction, but so far
+they’re only used opportunistically, based on workload. With the
+development of intel_powerclamp driver, the method of synchronizing
+idle injection across all online CPU threads was introduced. The goal
+is to achieve forced and controllable C-state residency.
+
+Test/Analysis has been made in the areas of power, performance,
+scalability, and user experience. In many cases, clear advantage is
+shown over taking the CPU offline or modulating the CPU clock.
+
+
+===================
+THEORY OF OPERATION
+===================
+
+Idle Injection
+--------------
+
+On modern Intel processors (Nehalem or later), package level C-state
+residency is available in MSRs, thus also available to the kernel.
+
+These MSRs are:
+      #define MSR_PKG_C2_RESIDENCY	0x60D
+      #define MSR_PKG_C3_RESIDENCY	0x3F8
+      #define MSR_PKG_C6_RESIDENCY	0x3F9
+      #define MSR_PKG_C7_RESIDENCY	0x3FA
+
+If the kernel can also inject idle time to the system, then a
+closed-loop control system can be established that manages package
+level C-state. The intel_powerclamp driver is conceived as such a
+control system, where the target set point is a user-selected idle
+ratio (based on power reduction), and the error is the difference
+between the actual package level C-state residency ratio and the target idle
+ratio.
+
+Injection is controlled by high priority kernel threads, spawned for
+each online CPU.
+
+These kernel threads, with SCHED_FIFO class, are created to perform
+clamping actions of controlled duty ratio and duration. Each per-CPU
+thread synchronizes its idle time and duration, based on the rounding
+of jiffies, so accumulated errors can be prevented to avoid a jittery
+effect. Threads are also bound to the CPU such that they cannot be
+migrated, unless the CPU is taken offline. In this case, threads
+belong to the offlined CPUs will be terminated immediately.
+
+Running as SCHED_FIFO and relatively high priority, also allows such
+scheme to work for both preemptable and non-preemptable kernels.
+Alignment of idle time around jiffies ensures scalability for HZ
+values. This effect can be better visualized using a Perf timechart.
+The following diagram shows the behavior of kernel thread
+kidle_inject/cpu. During idle injection, it runs monitor/mwait idle
+for a given "duration", then relinquishes the CPU to other tasks,
+until the next time interval.
+
+The NOHZ schedule tick is disabled during idle time, but interrupts
+are not masked. Tests show that the extra wakeups from scheduler tick
+have a dramatic impact on the effectiveness of the powerclamp driver
+on large scale systems (Westmere system with 80 processors).
+
+CPU0
+		  ____________          ____________
+kidle_inject/0   |   sleep    |  mwait |  sleep     |
+	_________|            |________|            |_______
+			       duration
+CPU1
+		  ____________          ____________
+kidle_inject/1   |   sleep    |  mwait |  sleep     |
+	_________|            |________|            |_______
+			      ^
+			      |
+			      |
+			      roundup(jiffies, interval)
+
+Only one CPU is allowed to collect statistics and update global
+control parameters. This CPU is referred to as the controlling CPU in
+this document. The controlling CPU is elected at runtime, with a
+policy that favors BSP, taking into account the possibility of a CPU
+hot-plug.
+
+In terms of dynamics of the idle control system, package level idle
+time is considered largely as a non-causal system where its behavior
+cannot be based on the past or current input. Therefore, the
+intel_powerclamp driver attempts to enforce the desired idle time
+instantly as given input (target idle ratio). After injection,
+powerclamp moniors the actual idle for a given time window and adjust
+the next injection accordingly to avoid over/under correction.
+
+When used in a causal control system, such as a temperature control,
+it is up to the user of this driver to implement algorithms where
+past samples and outputs are included in the feedback. For example, a
+PID-based thermal controller can use the powerclamp driver to
+maintain a desired target temperature, based on integral and
+derivative gains of the past samples.
+
+
+
+Calibration
+-----------
+During scalability testing, it is observed that synchronized actions
+among CPUs become challenging as the number of cores grows. This is
+also true for the ability of a system to enter package level C-states.
+
+To make sure the intel_powerclamp driver scales well, online
+calibration is implemented. The goals for doing such a calibration
+are:
+
+a) determine the effective range of idle injection ratio
+b) determine the amount of compensation needed at each target ratio
+
+Compensation to each target ratio consists of two parts:
+
+        a) steady state error compensation
+	This is to offset the error occurring when the system can
+	enter idle without extra wakeups (such as external interrupts).
+
+	b) dynamic error compensation
+	When an excessive amount of wakeups occurs during idle, an
+	additional idle ratio can be added to quiet interrupts, by
+	slowing down CPU activities.
+
+A debugfs file is provided for the user to examine compensation
+progress and results, such as on a Westmere system.
+[jacob@nex01 ~]$ cat
+/sys/kernel/debug/intel_powerclamp/powerclamp_calib
+controlling cpu: 0
+pct confidence steady dynamic (compensation)
+0	0	0	0
+1	1	0	0
+2	1	1	0
+3	3	1	0
+4	3	1	0
+5	3	1	0
+6	3	1	0
+7	3	1	0
+8	3	1	0
+...
+30	3	2	0
+31	3	2	0
+32	3	1	0
+33	3	2	0
+34	3	1	0
+35	3	2	0
+36	3	1	0
+37	3	2	0
+38	3	1	0
+39	3	2	0
+40	3	3	0
+41	3	1	0
+42	3	2	0
+43	3	1	0
+44	3	1	0
+45	3	2	0
+46	3	3	0
+47	3	0	0
+48	3	2	0
+49	3	3	0
+
+Calibration occurs during runtime. No offline method is available.
+Steady state compensation is used only when confidence levels of all
+adjacent ratios have reached satisfactory level. A confidence level
+is accumulated based on clean data collected at runtime. Data
+collected during a period without extra interrupts is considered
+clean.
+
+To compensate for excessive amounts of wakeup during idle, additional
+idle time is injected when such a condition is detected. Currently,
+we have a simple algorithm to double the injection ratio. A possible
+enhancement might be to throttle the offending IRQ, such as delaying
+EOI for level triggered interrupts. But it is a challenge to be
+non-intrusive to the scheduler or the IRQ core code.
+
+
+CPU Online/Offline
+------------------
+Per-CPU kernel threads are started/stopped upon receiving
+notifications of CPU hotplug activities. The intel_powerclamp driver
+keeps track of clamping kernel threads, even after they are migrated
+to other CPUs, after a CPU offline event.
+
+
+=====================
+Performance Analysis
+=====================
+This section describes the general performance data collected on
+multiple systems, including Westmere (80P) and Ivy Bridge (4P, 8P).
+
+Effectiveness and Limitations
+-----------------------------
+The maximum range that idle injection is allowed is capped at 50
+percent. As mentioned earlier, since interrupts are allowed during
+forced idle time, excessive interrupts could result in less
+effectiveness. The extreme case would be doing a ping -f to generated
+flooded network interrupts without much CPU acknowledgement. In this
+case, little can be done from the idle injection threads. In most
+normal cases, such as scp a large file, applications can be throttled
+by the powerclamp driver, since slowing down the CPU also slows down
+network protocol processing, which in turn reduces interrupts.
+
+When control parameters change at runtime by the controlling CPU, it
+may take an additional period for the rest of the CPUs to catch up
+with the changes. During this time, idle injection is out of sync,
+thus not able to enter package C- states at the expected ratio. But
+this effect is minor, in that in most cases change to the target
+ratio is updated much less frequently than the idle injection
+frequency.
+
+Scalability
+-----------
+Tests also show a minor, but measurable, difference between the 4P/8P
+Ivy Bridge system and the 80P Westmere server under 50% idle ratio.
+More compensation is needed on Westmere for the same amount of
+target idle ratio. The compensation also increases as the idle ratio
+gets larger. The above reason constitutes the need for the
+calibration code.
+
+On the IVB 8P system, compared to an offline CPU, powerclamp can
+achieve up to 40% better performance per watt. (measured by a spin
+counter summed over per CPU counting threads spawned for all running
+CPUs).
+
+====================
+Usage and Interfaces
+====================
+The powerclamp driver is registered to the generic thermal layer as a
+cooling device. Currently, it’s not bound to any thermal zones.
+
+jacob@chromoly:/sys/class/thermal/cooling_device14$ grep . *
+cur_state:0
+max_state:50
+type:intel_powerclamp
+
+Example usage:
+- To inject 25% idle time
+$ sudo sh -c "echo 25 > /sys/class/thermal/cooling_device80/cur_state
+"
+
+If the system is not busy and has more than 25% idle time already,
+then the powerclamp driver will not start idle injection. Using Top
+will not show idle injection kernel threads.
+
+If the system is busy (spin test below) and has less than 25% natural
+idle time, powerclamp kernel threads will do idle injection, which
+appear running to the scheduler. But the overall system idle is still
+reflected. In this example, 24.1% idle is shown. This helps the
+system admin or user determine the cause of slowdown, when a
+powerclamp driver is in action.
+
+
+Tasks: 197 total,   1 running, 196 sleeping,   0 stopped,   0 zombie
+Cpu(s): 71.2%us,  4.7%sy,  0.0%ni, 24.1%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
+Mem:   3943228k total,  1689632k used,  2253596k free,    74960k buffers
+Swap:  4087804k total,        0k used,  4087804k free,   945336k cached
+
+  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
+ 3352 jacob     20   0  262m  644  428 S  286  0.0   0:17.16 spin
+ 3341 root     -51   0     0    0    0 D   25  0.0   0:01.62 kidle_inject/0
+ 3344 root     -51   0     0    0    0 D   25  0.0   0:01.60 kidle_inject/3
+ 3342 root     -51   0     0    0    0 D   25  0.0   0:01.61 kidle_inject/1
+ 3343 root     -51   0     0    0    0 D   25  0.0   0:01.60 kidle_inject/2
+ 2935 jacob     20   0  696m 125m  35m S    5  3.3   0:31.11 firefox
+ 1546 root      20   0  158m  20m 6640 S    3  0.5   0:26.97 Xorg
+ 2100 jacob     20   0 1223m  88m  30m S    3  2.3   0:23.68 compiz
+
+Tests have shown that by using the powerclamp driver as a cooling
+device, a PID based userspace thermal controller can manage to
+control CPU temperature effectively, when no other thermal influence
+is added. For example, a UltraBook user can compile the kernel under
+certain temperature (below most active trip points).
diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
index c31b9e4..faf38c5 100644
--- a/drivers/thermal/Kconfig
+++ b/drivers/thermal/Kconfig
@@ -131,4 +131,14 @@
 	  bound cpufreq cooling device turns active to set CPU frequency low to
 	  cool down the CPU.
 
+config INTEL_POWERCLAMP
+	tristate "Intel PowerClamp idle injection driver"
+	depends on THERMAL
+	depends on X86
+	depends on CPU_SUP_INTEL
+	help
+	  Enable this to enable Intel PowerClamp idle injection driver. This
+	  enforce idle time which results in more package C-state residency. The
+	  user interface is exposed via generic thermal framework.
+
 endif
diff --git a/drivers/thermal/Makefile b/drivers/thermal/Makefile
index d8da683..574f5f5 100644
--- a/drivers/thermal/Makefile
+++ b/drivers/thermal/Makefile
@@ -18,3 +18,5 @@
 obj-$(CONFIG_EXYNOS_THERMAL)	+= exynos_thermal.o
 obj-$(CONFIG_DB8500_THERMAL)	+= db8500_thermal.o
 obj-$(CONFIG_DB8500_CPUFREQ_COOLING)	+= db8500_cpufreq_cooling.o
+obj-$(CONFIG_INTEL_POWERCLAMP)	+= intel_powerclamp.o
+
diff --git a/drivers/thermal/intel_powerclamp.c b/drivers/thermal/intel_powerclamp.c
new file mode 100644
index 0000000..a85ff38
--- /dev/null
+++ b/drivers/thermal/intel_powerclamp.c
@@ -0,0 +1,794 @@
+/*
+ * intel_powerclamp.c - package c-state idle injection
+ *
+ * Copyright (c) 2012, Intel Corporation.
+ *
+ * Authors:
+ *     Arjan van de Ven <arjan@linux.intel.com>
+ *     Jacob Pan <jacob.jun.pan@linux.intel.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope 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.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ *
+ *	TODO:
+ *           1. better handle wakeup from external interrupts, currently a fixed
+ *              compensation is added to clamping duration when excessive amount
+ *              of wakeups are observed during idle time. the reason is that in
+ *              case of external interrupts without need for ack, clamping down
+ *              cpu in non-irq context does not reduce irq. for majority of the
+ *              cases, clamping down cpu does help reduce irq as well, we should
+ *              be able to differenciate the two cases and give a quantitative
+ *              solution for the irqs that we can control. perhaps based on
+ *              get_cpu_iowait_time_us()
+ *
+ *	     2. synchronization with other hw blocks
+ *
+ *
+ */
+
+#define pr_fmt(fmt)	KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/freezer.h>
+#include <linux/cpu.h>
+#include <linux/thermal.h>
+#include <linux/slab.h>
+#include <linux/tick.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+
+#include <asm/nmi.h>
+#include <asm/msr.h>
+#include <asm/mwait.h>
+#include <asm/cpu_device_id.h>
+#include <asm/idle.h>
+#include <asm/hardirq.h>
+
+#define MAX_TARGET_RATIO (50U)
+/* For each undisturbed clamping period (no extra wake ups during idle time),
+ * we increment the confidence counter for the given target ratio.
+ * CONFIDENCE_OK defines the level where runtime calibration results are
+ * valid.
+ */
+#define CONFIDENCE_OK (3)
+/* Default idle injection duration, driver adjust sleep time to meet target
+ * idle ratio. Similar to frequency modulation.
+ */
+#define DEFAULT_DURATION_JIFFIES (6)
+
+static unsigned int target_mwait;
+static struct dentry *debug_dir;
+
+/* user selected target */
+static unsigned int set_target_ratio;
+static unsigned int current_ratio;
+static bool should_skip;
+static bool reduce_irq;
+static atomic_t idle_wakeup_counter;
+static unsigned int control_cpu; /* The cpu assigned to collect stat and update
+				  * control parameters. default to BSP but BSP
+				  * can be offlined.
+				  */
+static bool clamping;
+
+
+static struct task_struct * __percpu *powerclamp_thread;
+static struct thermal_cooling_device *cooling_dev;
+static unsigned long *cpu_clamping_mask;  /* bit map for tracking per cpu
+					   * clamping thread
+					   */
+
+static unsigned int duration;
+static unsigned int pkg_cstate_ratio_cur;
+static unsigned int window_size;
+
+static int duration_set(const char *arg, const struct kernel_param *kp)
+{
+	int ret = 0;
+	unsigned long new_duration;
+
+	ret = kstrtoul(arg, 10, &new_duration);
+	if (ret)
+		goto exit;
+	if (new_duration > 25 || new_duration < 6) {
+		pr_err("Out of recommended range %lu, between 6-25ms\n",
+			new_duration);
+		ret = -EINVAL;
+	}
+
+	duration = clamp(new_duration, 6ul, 25ul);
+	smp_mb();
+
+exit:
+
+	return ret;
+}
+
+static struct kernel_param_ops duration_ops = {
+	.set = duration_set,
+	.get = param_get_int,
+};
+
+
+module_param_cb(duration, &duration_ops, &duration, 0644);
+MODULE_PARM_DESC(duration, "forced idle time for each attempt in msec.");
+
+struct powerclamp_calibration_data {
+	unsigned long confidence;  /* used for calibration, basically a counter
+				    * gets incremented each time a clamping
+				    * period is completed without extra wakeups
+				    * once that counter is reached given level,
+				    * compensation is deemed usable.
+				    */
+	unsigned long steady_comp; /* steady state compensation used when
+				    * no extra wakeups occurred.
+				    */
+	unsigned long dynamic_comp; /* compensate excessive wakeup from idle
+				     * mostly from external interrupts.
+				     */
+};
+
+static struct powerclamp_calibration_data cal_data[MAX_TARGET_RATIO];
+
+static int window_size_set(const char *arg, const struct kernel_param *kp)
+{
+	int ret = 0;
+	unsigned long new_window_size;
+
+	ret = kstrtoul(arg, 10, &new_window_size);
+	if (ret)
+		goto exit_win;
+	if (new_window_size > 10 || new_window_size < 2) {
+		pr_err("Out of recommended window size %lu, between 2-10\n",
+			new_window_size);
+		ret = -EINVAL;
+	}
+
+	window_size = clamp(new_window_size, 2ul, 10ul);
+	smp_mb();
+
+exit_win:
+
+	return ret;
+}
+
+static struct kernel_param_ops window_size_ops = {
+	.set = window_size_set,
+	.get = param_get_int,
+};
+
+module_param_cb(window_size, &window_size_ops, &window_size, 0644);
+MODULE_PARM_DESC(window_size, "sliding window in number of clamping cycles\n"
+	"\tpowerclamp controls idle ratio within this window. larger\n"
+	"\twindow size results in slower response time but more smooth\n"
+	"\tclamping results. default to 2.");
+
+static void find_target_mwait(void)
+{
+	unsigned int eax, ebx, ecx, edx;
+	unsigned int highest_cstate = 0;
+	unsigned int highest_subcstate = 0;
+	int i;
+
+	if (boot_cpu_data.cpuid_level < CPUID_MWAIT_LEAF)
+		return;
+
+	cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx);
+
+	if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED) ||
+	    !(ecx & CPUID5_ECX_INTERRUPT_BREAK))
+		return;
+
+	edx >>= MWAIT_SUBSTATE_SIZE;
+	for (i = 0; i < 7 && edx; i++, edx >>= MWAIT_SUBSTATE_SIZE) {
+		if (edx & MWAIT_SUBSTATE_MASK) {
+			highest_cstate = i;
+			highest_subcstate = edx & MWAIT_SUBSTATE_MASK;
+		}
+	}
+	target_mwait = (highest_cstate << MWAIT_SUBSTATE_SIZE) |
+		(highest_subcstate - 1);
+
+}
+
+static u64 pkg_state_counter(void)
+{
+	u64 val;
+	u64 count = 0;
+
+	static bool skip_c2;
+	static bool skip_c3;
+	static bool skip_c6;
+	static bool skip_c7;
+
+	if (!skip_c2) {
+		if (!rdmsrl_safe(MSR_PKG_C2_RESIDENCY, &val))
+			count += val;
+		else
+			skip_c2 = true;
+	}
+
+	if (!skip_c3) {
+		if (!rdmsrl_safe(MSR_PKG_C3_RESIDENCY, &val))
+			count += val;
+		else
+			skip_c3 = true;
+	}
+
+	if (!skip_c6) {
+		if (!rdmsrl_safe(MSR_PKG_C6_RESIDENCY, &val))
+			count += val;
+		else
+			skip_c6 = true;
+	}
+
+	if (!skip_c7) {
+		if (!rdmsrl_safe(MSR_PKG_C7_RESIDENCY, &val))
+			count += val;
+		else
+			skip_c7 = true;
+	}
+
+	return count;
+}
+
+static void noop_timer(unsigned long foo)
+{
+	/* empty... just the fact that we get the interrupt wakes us up */
+}
+
+static unsigned int get_compensation(int ratio)
+{
+	unsigned int comp = 0;
+
+	/* we only use compensation if all adjacent ones are good */
+	if (ratio == 1 &&
+		cal_data[ratio].confidence >= CONFIDENCE_OK &&
+		cal_data[ratio + 1].confidence >= CONFIDENCE_OK &&
+		cal_data[ratio + 2].confidence >= CONFIDENCE_OK) {
+		comp = (cal_data[ratio].steady_comp +
+			cal_data[ratio + 1].steady_comp +
+			cal_data[ratio + 2].steady_comp) / 3;
+	} else if (ratio == MAX_TARGET_RATIO - 1 &&
+		cal_data[ratio].confidence >= CONFIDENCE_OK &&
+		cal_data[ratio - 1].confidence >= CONFIDENCE_OK &&
+		cal_data[ratio - 2].confidence >= CONFIDENCE_OK) {
+		comp = (cal_data[ratio].steady_comp +
+			cal_data[ratio - 1].steady_comp +
+			cal_data[ratio - 2].steady_comp) / 3;
+	} else if (cal_data[ratio].confidence >= CONFIDENCE_OK &&
+		cal_data[ratio - 1].confidence >= CONFIDENCE_OK &&
+		cal_data[ratio + 1].confidence >= CONFIDENCE_OK) {
+		comp = (cal_data[ratio].steady_comp +
+			cal_data[ratio - 1].steady_comp +
+			cal_data[ratio + 1].steady_comp) / 3;
+	}
+
+	/* REVISIT: simple penalty of double idle injection */
+	if (reduce_irq)
+		comp = ratio;
+	/* do not exceed limit */
+	if (comp + ratio >= MAX_TARGET_RATIO)
+		comp = MAX_TARGET_RATIO - ratio - 1;
+
+	return comp;
+}
+
+static void adjust_compensation(int target_ratio, unsigned int win)
+{
+	int delta;
+	struct powerclamp_calibration_data *d = &cal_data[target_ratio];
+
+	/*
+	 * adjust compensations if confidence level has not been reached or
+	 * there are too many wakeups during the last idle injection period, we
+	 * cannot trust the data for compensation.
+	 */
+	if (d->confidence >= CONFIDENCE_OK ||
+		atomic_read(&idle_wakeup_counter) >
+		win * num_online_cpus())
+		return;
+
+	delta = set_target_ratio - current_ratio;
+	/* filter out bad data */
+	if (delta >= 0 && delta <= (1+target_ratio/10)) {
+		if (d->steady_comp)
+			d->steady_comp =
+				roundup(delta+d->steady_comp, 2)/2;
+		else
+			d->steady_comp = delta;
+		d->confidence++;
+	}
+}
+
+static bool powerclamp_adjust_controls(unsigned int target_ratio,
+				unsigned int guard, unsigned int win)
+{
+	static u64 msr_last, tsc_last;
+	u64 msr_now, tsc_now;
+	u64 val64;
+
+	/* check result for the last window */
+	msr_now = pkg_state_counter();
+	rdtscll(tsc_now);
+
+	/* calculate pkg cstate vs tsc ratio */
+	if (!msr_last || !tsc_last)
+		current_ratio = 1;
+	else if (tsc_now-tsc_last) {
+		val64 = 100*(msr_now-msr_last);
+		do_div(val64, (tsc_now-tsc_last));
+		current_ratio = val64;
+	}
+
+	/* update record */
+	msr_last = msr_now;
+	tsc_last = tsc_now;
+
+	adjust_compensation(target_ratio, win);
+	/*
+	 * too many external interrupts, set flag such
+	 * that we can take measure later.
+	 */
+	reduce_irq = atomic_read(&idle_wakeup_counter) >=
+		2 * win * num_online_cpus();
+
+	atomic_set(&idle_wakeup_counter, 0);
+	/* if we are above target+guard, skip */
+	return set_target_ratio + guard <= current_ratio;
+}
+
+static int clamp_thread(void *arg)
+{
+	int cpunr = (unsigned long)arg;
+	DEFINE_TIMER(wakeup_timer, noop_timer, 0, 0);
+	static const struct sched_param param = {
+		.sched_priority = MAX_USER_RT_PRIO/2,
+	};
+	unsigned int count = 0;
+	unsigned int target_ratio;
+
+	set_bit(cpunr, cpu_clamping_mask);
+	set_freezable();
+	init_timer_on_stack(&wakeup_timer);
+	sched_setscheduler(current, SCHED_FIFO, &param);
+
+	while (true == clamping && !kthread_should_stop() &&
+		cpu_online(cpunr)) {
+		int sleeptime;
+		unsigned long target_jiffies;
+		unsigned int guard;
+		unsigned int compensation = 0;
+		int interval; /* jiffies to sleep for each attempt */
+		unsigned int duration_jiffies = msecs_to_jiffies(duration);
+		unsigned int window_size_now;
+
+		try_to_freeze();
+		/*
+		 * make sure user selected ratio does not take effect until
+		 * the next round. adjust target_ratio if user has changed
+		 * target such that we can converge quickly.
+		 */
+		target_ratio = set_target_ratio;
+		guard = 1 + target_ratio/20;
+		window_size_now = window_size;
+		count++;
+
+		/*
+		 * systems may have different ability to enter package level
+		 * c-states, thus we need to compensate the injected idle ratio
+		 * to achieve the actual target reported by the HW.
+		 */
+		compensation = get_compensation(target_ratio);
+		interval = duration_jiffies*100/(target_ratio+compensation);
+
+		/* align idle time */
+		target_jiffies = roundup(jiffies, interval);
+		sleeptime = target_jiffies - jiffies;
+		if (sleeptime <= 0)
+			sleeptime = 1;
+		schedule_timeout_interruptible(sleeptime);
+		/*
+		 * only elected controlling cpu can collect stats and update
+		 * control parameters.
+		 */
+		if (cpunr == control_cpu && !(count%window_size_now)) {
+			should_skip =
+				powerclamp_adjust_controls(target_ratio,
+							guard, window_size_now);
+			smp_mb();
+		}
+
+		if (should_skip)
+			continue;
+
+		target_jiffies = jiffies + duration_jiffies;
+		mod_timer(&wakeup_timer, target_jiffies);
+		if (unlikely(local_softirq_pending()))
+			continue;
+		/*
+		 * stop tick sched during idle time, interrupts are still
+		 * allowed. thus jiffies are updated properly.
+		 */
+		preempt_disable();
+		tick_nohz_idle_enter();
+		/* mwait until target jiffies is reached */
+		while (time_before(jiffies, target_jiffies)) {
+			unsigned long ecx = 1;
+			unsigned long eax = target_mwait;
+
+			/*
+			 * REVISIT: may call enter_idle() to notify drivers who
+			 * can save power during cpu idle. same for exit_idle()
+			 */
+			local_touch_nmi();
+			stop_critical_timings();
+			__monitor((void *)&current_thread_info()->flags, 0, 0);
+			cpu_relax(); /* allow HT sibling to run */
+			__mwait(eax, ecx);
+			start_critical_timings();
+			atomic_inc(&idle_wakeup_counter);
+		}
+		tick_nohz_idle_exit();
+		preempt_enable_no_resched();
+	}
+	del_timer_sync(&wakeup_timer);
+	clear_bit(cpunr, cpu_clamping_mask);
+
+	return 0;
+}
+
+/*
+ * 1 HZ polling while clamping is active, useful for userspace
+ * to monitor actual idle ratio.
+ */
+static void poll_pkg_cstate(struct work_struct *dummy);
+static DECLARE_DELAYED_WORK(poll_pkg_cstate_work, poll_pkg_cstate);
+static void poll_pkg_cstate(struct work_struct *dummy)
+{
+	static u64 msr_last;
+	static u64 tsc_last;
+	static unsigned long jiffies_last;
+
+	u64 msr_now;
+	unsigned long jiffies_now;
+	u64 tsc_now;
+	u64 val64;
+
+	msr_now = pkg_state_counter();
+	rdtscll(tsc_now);
+	jiffies_now = jiffies;
+
+	/* calculate pkg cstate vs tsc ratio */
+	if (!msr_last || !tsc_last)
+		pkg_cstate_ratio_cur = 1;
+	else {
+		if (tsc_now - tsc_last) {
+			val64 = 100 * (msr_now - msr_last);
+			do_div(val64, (tsc_now - tsc_last));
+			pkg_cstate_ratio_cur = val64;
+		}
+	}
+
+	/* update record */
+	msr_last = msr_now;
+	jiffies_last = jiffies_now;
+	tsc_last = tsc_now;
+
+	if (true == clamping)
+		schedule_delayed_work(&poll_pkg_cstate_work, HZ);
+}
+
+static int start_power_clamp(void)
+{
+	unsigned long cpu;
+	struct task_struct *thread;
+
+	/* check if pkg cstate counter is completely 0, abort in this case */
+	if (!pkg_state_counter()) {
+		pr_err("pkg cstate counter not functional, abort\n");
+		return -EINVAL;
+	}
+
+	set_target_ratio = clamp(set_target_ratio, 0U, MAX_TARGET_RATIO);
+	/* prevent cpu hotplug */
+	get_online_cpus();
+
+	/* prefer BSP */
+	control_cpu = 0;
+	if (!cpu_online(control_cpu))
+		control_cpu = smp_processor_id();
+
+	clamping = true;
+	schedule_delayed_work(&poll_pkg_cstate_work, 0);
+
+	/* start one thread per online cpu */
+	for_each_online_cpu(cpu) {
+		struct task_struct **p =
+			per_cpu_ptr(powerclamp_thread, cpu);
+
+		thread = kthread_create_on_node(clamp_thread,
+						(void *) cpu,
+						cpu_to_node(cpu),
+						"kidle_inject/%ld", cpu);
+		/* bind to cpu here */
+		if (likely(!IS_ERR(thread))) {
+			kthread_bind(thread, cpu);
+			wake_up_process(thread);
+			*p = thread;
+		}
+
+	}
+	put_online_cpus();
+
+	return 0;
+}
+
+static void end_power_clamp(void)
+{
+	int i;
+	struct task_struct *thread;
+
+	clamping = false;
+	/*
+	 * make clamping visible to other cpus and give per cpu clamping threads
+	 * sometime to exit, or gets killed later.
+	 */
+	smp_mb();
+	msleep(20);
+	if (bitmap_weight(cpu_clamping_mask, num_possible_cpus())) {
+		for_each_set_bit(i, cpu_clamping_mask, num_possible_cpus()) {
+			pr_debug("clamping thread for cpu %d alive, kill\n", i);
+			thread = *per_cpu_ptr(powerclamp_thread, i);
+			kthread_stop(thread);
+		}
+	}
+}
+
+static int powerclamp_cpu_callback(struct notifier_block *nfb,
+				unsigned long action, void *hcpu)
+{
+	unsigned long cpu = (unsigned long)hcpu;
+	struct task_struct *thread;
+	struct task_struct **percpu_thread =
+		per_cpu_ptr(powerclamp_thread, cpu);
+
+	if (false == clamping)
+		goto exit_ok;
+
+	switch (action) {
+	case CPU_ONLINE:
+		thread = kthread_create_on_node(clamp_thread,
+						(void *) cpu,
+						cpu_to_node(cpu),
+						"kidle_inject/%lu", cpu);
+		if (likely(!IS_ERR(thread))) {
+			kthread_bind(thread, cpu);
+			wake_up_process(thread);
+			*percpu_thread = thread;
+		}
+		/* prefer BSP as controlling CPU */
+		if (cpu == 0) {
+			control_cpu = 0;
+			smp_mb();
+		}
+		break;
+	case CPU_DEAD:
+		if (test_bit(cpu, cpu_clamping_mask)) {
+			pr_err("cpu %lu dead but powerclamping thread is not\n",
+				cpu);
+			kthread_stop(*percpu_thread);
+		}
+		if (cpu == control_cpu) {
+			control_cpu = smp_processor_id();
+			smp_mb();
+		}
+	}
+
+exit_ok:
+	return NOTIFY_OK;
+}
+
+static struct notifier_block powerclamp_cpu_notifier = {
+	.notifier_call = powerclamp_cpu_callback,
+};
+
+static int powerclamp_get_max_state(struct thermal_cooling_device *cdev,
+				 unsigned long *state)
+{
+	*state = MAX_TARGET_RATIO;
+
+	return 0;
+}
+
+static int powerclamp_get_cur_state(struct thermal_cooling_device *cdev,
+				 unsigned long *state)
+{
+	if (true == clamping)
+		*state = pkg_cstate_ratio_cur;
+	else
+		/* to save power, do not poll idle ratio while not clamping */
+		*state = -1; /* indicates invalid state */
+
+	return 0;
+}
+
+static int powerclamp_set_cur_state(struct thermal_cooling_device *cdev,
+				 unsigned long new_target_ratio)
+{
+	int ret = 0;
+
+	new_target_ratio = clamp(new_target_ratio, 0UL,
+				(unsigned long) (MAX_TARGET_RATIO-1));
+	if (set_target_ratio == 0 && new_target_ratio > 0) {
+		pr_info("Start idle injection to reduce power\n");
+		set_target_ratio = new_target_ratio;
+		ret = start_power_clamp();
+		goto exit_set;
+	} else	if (set_target_ratio > 0 && new_target_ratio == 0) {
+		pr_info("Stop forced idle injection\n");
+		set_target_ratio = 0;
+		end_power_clamp();
+	} else	/* adjust currently running */ {
+		set_target_ratio = new_target_ratio;
+		/* make new set_target_ratio visible to other cpus */
+		smp_mb();
+	}
+
+exit_set:
+	return ret;
+}
+
+/* bind to generic thermal layer as cooling device*/
+static struct thermal_cooling_device_ops powerclamp_cooling_ops = {
+	.get_max_state = powerclamp_get_max_state,
+	.get_cur_state = powerclamp_get_cur_state,
+	.set_cur_state = powerclamp_set_cur_state,
+};
+
+/* runs on Nehalem and later */
+static const struct x86_cpu_id intel_powerclamp_ids[] = {
+	{ X86_VENDOR_INTEL, 6, 0x1a},
+	{ X86_VENDOR_INTEL, 6, 0x1c},
+	{ X86_VENDOR_INTEL, 6, 0x1e},
+	{ X86_VENDOR_INTEL, 6, 0x1f},
+	{ X86_VENDOR_INTEL, 6, 0x25},
+	{ X86_VENDOR_INTEL, 6, 0x26},
+	{ X86_VENDOR_INTEL, 6, 0x2a},
+	{ X86_VENDOR_INTEL, 6, 0x2c},
+	{ X86_VENDOR_INTEL, 6, 0x2d},
+	{ X86_VENDOR_INTEL, 6, 0x2e},
+	{ X86_VENDOR_INTEL, 6, 0x2f},
+	{ X86_VENDOR_INTEL, 6, 0x3a},
+	{}
+};
+MODULE_DEVICE_TABLE(x86cpu, intel_powerclamp_ids);
+
+static int powerclamp_probe(void)
+{
+	if (!x86_match_cpu(intel_powerclamp_ids)) {
+		pr_err("Intel powerclamp does not run on family %d model %d\n",
+				boot_cpu_data.x86, boot_cpu_data.x86_model);
+		return -ENODEV;
+	}
+	if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC) ||
+		!boot_cpu_has(X86_FEATURE_CONSTANT_TSC) ||
+		!boot_cpu_has(X86_FEATURE_MWAIT) ||
+		!boot_cpu_has(X86_FEATURE_ARAT))
+		return -ENODEV;
+
+	/* find the deepest mwait value */
+	find_target_mwait();
+
+	return 0;
+}
+
+static int powerclamp_debug_show(struct seq_file *m, void *unused)
+{
+	int i = 0;
+
+	seq_printf(m, "controlling cpu: %d\n", control_cpu);
+	seq_printf(m, "pct confidence steady dynamic (compensation)\n");
+	for (i = 0; i < MAX_TARGET_RATIO; i++) {
+		seq_printf(m, "%d\t%lu\t%lu\t%lu\n",
+			i,
+			cal_data[i].confidence,
+			cal_data[i].steady_comp,
+			cal_data[i].dynamic_comp);
+	}
+
+	return 0;
+}
+
+static int powerclamp_debug_open(struct inode *inode,
+			struct file *file)
+{
+	return single_open(file, powerclamp_debug_show, inode->i_private);
+}
+
+static const struct file_operations powerclamp_debug_fops = {
+	.open		= powerclamp_debug_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+	.owner		= THIS_MODULE,
+};
+
+static inline void powerclamp_create_debug_files(void)
+{
+	debug_dir = debugfs_create_dir("intel_powerclamp", NULL);
+	if (!debug_dir)
+		return;
+
+	if (!debugfs_create_file("powerclamp_calib", S_IRUGO, debug_dir,
+					cal_data, &powerclamp_debug_fops))
+		goto file_error;
+
+	return;
+
+file_error:
+	debugfs_remove_recursive(debug_dir);
+}
+
+static int powerclamp_init(void)
+{
+	int retval;
+	int bitmap_size;
+
+	bitmap_size = BITS_TO_LONGS(num_possible_cpus()) * sizeof(long);
+	cpu_clamping_mask = kzalloc(bitmap_size, GFP_KERNEL);
+	if (!cpu_clamping_mask)
+		return -ENOMEM;
+
+	/* probe cpu features and ids here */
+	retval = powerclamp_probe();
+	if (retval)
+		return retval;
+	/* set default limit, maybe adjusted during runtime based on feedback */
+	window_size = 2;
+	register_hotcpu_notifier(&powerclamp_cpu_notifier);
+	powerclamp_thread = alloc_percpu(struct task_struct *);
+	cooling_dev = thermal_cooling_device_register("intel_powerclamp", NULL,
+						&powerclamp_cooling_ops);
+	if (IS_ERR(cooling_dev))
+		return -ENODEV;
+
+	if (!duration)
+		duration = jiffies_to_msecs(DEFAULT_DURATION_JIFFIES);
+	powerclamp_create_debug_files();
+
+	return 0;
+}
+module_init(powerclamp_init);
+
+static void powerclamp_exit(void)
+{
+	unregister_hotcpu_notifier(&powerclamp_cpu_notifier);
+	end_power_clamp();
+	free_percpu(powerclamp_thread);
+	thermal_cooling_device_unregister(cooling_dev);
+	kfree(cpu_clamping_mask);
+
+	cancel_delayed_work_sync(&poll_pkg_cstate_work);
+	debugfs_remove_recursive(debug_dir);
+}
+module_exit(powerclamp_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Arjan van de Ven <arjan@linux.intel.com>");
+MODULE_AUTHOR("Jacob Pan <jacob.jun.pan@linux.intel.com>");
+MODULE_DESCRIPTION("Package Level C-state Idle Injection for Intel CPUs");