diff --git a/MAINTAINERS b/MAINTAINERS
index 737a9b2..09a2028 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -257,6 +257,13 @@
 S:	Supported
 F:	drivers/acpi/fan.c
 
+ACPI PROCESSOR AGGREGATOR DRIVER
+M:	Shaohua Li <shaohua.li@intel.com>
+L:	linux-acpi@vger.kernel.org
+W:	http://www.lesswatts.org/projects/acpi/
+S:	Supported
+F:	drivers/acpi/acpi_pad.c
+
 ACPI THERMAL DRIVER
 M:	Zhang Rui <rui.zhang@intel.com>
 L:	linux-acpi@vger.kernel.org
diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index dd8729d..0ed42d8 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -211,6 +211,18 @@
 	select ACPI_CONTAINER
 	default y
 
+config ACPI_PROCESSOR_AGGREGATOR
+	tristate "Processor Aggregator"
+	depends on ACPI_PROCESSOR
+	depends on EXPERIMENTAL
+	depends on X86
+	help
+	  ACPI 4.0 defines processor Aggregator, which enables OS to perform
+	  specfic processor configuration and control that applies to all
+	  processors in the platform. Currently only logical processor idling
+	  is defined, which is to reduce power consumption. This driver
+	  support the new device.
+
 config ACPI_THERMAL
 	tristate "Thermal Zone"
 	depends on ACPI_PROCESSOR
diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
index 82cd49d..7702118 100644
--- a/drivers/acpi/Makefile
+++ b/drivers/acpi/Makefile
@@ -62,3 +62,5 @@
 processor-y			:= processor_core.o processor_throttling.o
 processor-y			+= processor_idle.o processor_thermal.o
 processor-$(CONFIG_CPU_FREQ)	+= processor_perflib.o
+
+obj-$(CONFIG_ACPI_PROCESSOR_AGGREGATOR) += acpi_pad.o
diff --git a/drivers/acpi/acpi_pad.c b/drivers/acpi/acpi_pad.c
new file mode 100644
index 0000000..0d2cdb8
--- /dev/null
+++ b/drivers/acpi/acpi_pad.c
@@ -0,0 +1,514 @@
+/*
+ * acpi_pad.c ACPI Processor Aggregator Driver
+ *
+ * Copyright (c) 2009, Intel Corporation.
+ *
+ * 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.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/cpumask.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/types.h>
+#include <linux/kthread.h>
+#include <linux/freezer.h>
+#include <linux/cpu.h>
+#include <linux/clockchips.h>
+#include <acpi/acpi_bus.h>
+#include <acpi/acpi_drivers.h>
+
+#define ACPI_PROCESSOR_AGGREGATOR_CLASS	"processor_aggregator"
+#define ACPI_PROCESSOR_AGGREGATOR_DEVICE_NAME "Processor Aggregator"
+#define ACPI_PROCESSOR_AGGREGATOR_NOTIFY 0x80
+static DEFINE_MUTEX(isolated_cpus_lock);
+
+#define MWAIT_SUBSTATE_MASK	(0xf)
+#define MWAIT_CSTATE_MASK	(0xf)
+#define MWAIT_SUBSTATE_SIZE	(4)
+#define CPUID_MWAIT_LEAF (5)
+#define CPUID5_ECX_EXTENSIONS_SUPPORTED (0x1)
+#define CPUID5_ECX_INTERRUPT_BREAK	(0x2)
+static unsigned long power_saving_mwait_eax;
+static void power_saving_mwait_init(void)
+{
+	unsigned int eax, ebx, ecx, edx;
+	unsigned int highest_cstate = 0;
+	unsigned int highest_subcstate = 0;
+	int i;
+
+	if (!boot_cpu_has(X86_FEATURE_MWAIT))
+		return;
+	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;
+		}
+	}
+	power_saving_mwait_eax = (highest_cstate << MWAIT_SUBSTATE_SIZE) |
+		(highest_subcstate - 1);
+
+	for_each_online_cpu(i)
+		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ON, &i);
+
+#if defined(CONFIG_GENERIC_TIME) && defined(CONFIG_X86)
+	switch (boot_cpu_data.x86_vendor) {
+	case X86_VENDOR_AMD:
+	case X86_VENDOR_INTEL:
+		/*
+		 * AMD Fam10h TSC will tick in all
+		 * C/P/S0/S1 states when this bit is set.
+		 */
+		if (boot_cpu_has(X86_FEATURE_NONSTOP_TSC))
+			return;
+
+		/*FALL THROUGH*/
+	default:
+		/* TSC could halt in idle, so notify users */
+		mark_tsc_unstable("TSC halts in idle");
+	}
+#endif
+}
+
+static unsigned long cpu_weight[NR_CPUS];
+static int tsk_in_cpu[NR_CPUS] = {[0 ... NR_CPUS-1] = -1};
+static DECLARE_BITMAP(pad_busy_cpus_bits, NR_CPUS);
+static void round_robin_cpu(unsigned int tsk_index)
+{
+	struct cpumask *pad_busy_cpus = to_cpumask(pad_busy_cpus_bits);
+	cpumask_var_t tmp;
+	int cpu;
+	unsigned long min_weight = -1, preferred_cpu;
+
+	if (!alloc_cpumask_var(&tmp, GFP_KERNEL))
+		return;
+
+	mutex_lock(&isolated_cpus_lock);
+	cpumask_clear(tmp);
+	for_each_cpu(cpu, pad_busy_cpus)
+		cpumask_or(tmp, tmp, topology_thread_cpumask(cpu));
+	cpumask_andnot(tmp, cpu_online_mask, tmp);
+	/* avoid HT sibilings if possible */
+	if (cpumask_empty(tmp))
+		cpumask_andnot(tmp, cpu_online_mask, pad_busy_cpus);
+	if (cpumask_empty(tmp)) {
+		mutex_unlock(&isolated_cpus_lock);
+		return;
+	}
+	for_each_cpu(cpu, tmp) {
+		if (cpu_weight[cpu] < min_weight) {
+			min_weight = cpu_weight[cpu];
+			preferred_cpu = cpu;
+		}
+	}
+
+	if (tsk_in_cpu[tsk_index] != -1)
+		cpumask_clear_cpu(tsk_in_cpu[tsk_index], pad_busy_cpus);
+	tsk_in_cpu[tsk_index] = preferred_cpu;
+	cpumask_set_cpu(preferred_cpu, pad_busy_cpus);
+	cpu_weight[preferred_cpu]++;
+	mutex_unlock(&isolated_cpus_lock);
+
+	set_cpus_allowed_ptr(current, cpumask_of(preferred_cpu));
+}
+
+static void exit_round_robin(unsigned int tsk_index)
+{
+	struct cpumask *pad_busy_cpus = to_cpumask(pad_busy_cpus_bits);
+	cpumask_clear_cpu(tsk_in_cpu[tsk_index], pad_busy_cpus);
+	tsk_in_cpu[tsk_index] = -1;
+}
+
+static unsigned int idle_pct = 5; /* percentage */
+static unsigned int round_robin_time = 10; /* second */
+static int power_saving_thread(void *data)
+{
+	struct sched_param param = {.sched_priority = 1};
+	int do_sleep;
+	unsigned int tsk_index = (unsigned long)data;
+	u64 last_jiffies = 0;
+
+	sched_setscheduler(current, SCHED_RR, &param);
+
+	while (!kthread_should_stop()) {
+		int cpu;
+		u64 expire_time;
+
+		try_to_freeze();
+
+		/* round robin to cpus */
+		if (last_jiffies + round_robin_time * HZ < jiffies) {
+			last_jiffies = jiffies;
+			round_robin_cpu(tsk_index);
+		}
+
+		do_sleep = 0;
+
+		current_thread_info()->status &= ~TS_POLLING;
+		/*
+		 * TS_POLLING-cleared state must be visible before we test
+		 * NEED_RESCHED:
+		 */
+		smp_mb();
+
+		expire_time = jiffies + HZ * (100 - idle_pct) / 100;
+
+		while (!need_resched()) {
+			local_irq_disable();
+			cpu = smp_processor_id();
+			clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER,
+				&cpu);
+			stop_critical_timings();
+
+			__monitor((void *)&current_thread_info()->flags, 0, 0);
+			smp_mb();
+			if (!need_resched())
+				__mwait(power_saving_mwait_eax, 1);
+
+			start_critical_timings();
+			clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT,
+				&cpu);
+			local_irq_enable();
+
+			if (jiffies > expire_time) {
+				do_sleep = 1;
+				break;
+			}
+		}
+
+		current_thread_info()->status |= TS_POLLING;
+
+		/*
+		 * current sched_rt has threshold for rt task running time.
+		 * When a rt task uses 95% CPU time, the rt thread will be
+		 * scheduled out for 5% CPU time to not starve other tasks. But
+		 * the mechanism only works when all CPUs have RT task running,
+		 * as if one CPU hasn't RT task, RT task from other CPUs will
+		 * borrow CPU time from this CPU and cause RT task use > 95%
+		 * CPU time. To make 'avoid staration' work, takes a nap here.
+		 */
+		if (do_sleep)
+			schedule_timeout_killable(HZ * idle_pct / 100);
+	}
+
+	exit_round_robin(tsk_index);
+	return 0;
+}
+
+static struct task_struct *ps_tsks[NR_CPUS];
+static unsigned int ps_tsk_num;
+static int create_power_saving_task(void)
+{
+	ps_tsks[ps_tsk_num] = kthread_run(power_saving_thread,
+		(void *)(unsigned long)ps_tsk_num,
+		"power_saving/%d", ps_tsk_num);
+	if (ps_tsks[ps_tsk_num]) {
+		ps_tsk_num++;
+		return 0;
+	}
+	return -EINVAL;
+}
+
+static void destroy_power_saving_task(void)
+{
+	if (ps_tsk_num > 0) {
+		ps_tsk_num--;
+		kthread_stop(ps_tsks[ps_tsk_num]);
+	}
+}
+
+static void set_power_saving_task_num(unsigned int num)
+{
+	if (num > ps_tsk_num) {
+		while (ps_tsk_num < num) {
+			if (create_power_saving_task())
+				return;
+		}
+	} else if (num < ps_tsk_num) {
+		while (ps_tsk_num > num)
+			destroy_power_saving_task();
+	}
+}
+
+static int acpi_pad_idle_cpus(unsigned int num_cpus)
+{
+	get_online_cpus();
+
+	num_cpus = min_t(unsigned int, num_cpus, num_online_cpus());
+	set_power_saving_task_num(num_cpus);
+
+	put_online_cpus();
+	return 0;
+}
+
+static uint32_t acpi_pad_idle_cpus_num(void)
+{
+	return ps_tsk_num;
+}
+
+static ssize_t acpi_pad_rrtime_store(struct device *dev,
+	struct device_attribute *attr, const char *buf, size_t count)
+{
+	unsigned long num;
+	if (strict_strtoul(buf, 0, &num))
+		return -EINVAL;
+	if (num < 1 || num >= 100)
+		return -EINVAL;
+	mutex_lock(&isolated_cpus_lock);
+	round_robin_time = num;
+	mutex_unlock(&isolated_cpus_lock);
+	return count;
+}
+
+static ssize_t acpi_pad_rrtime_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	return scnprintf(buf, PAGE_SIZE, "%d", round_robin_time);
+}
+static DEVICE_ATTR(rrtime, S_IRUGO|S_IWUSR,
+	acpi_pad_rrtime_show,
+	acpi_pad_rrtime_store);
+
+static ssize_t acpi_pad_idlepct_store(struct device *dev,
+	struct device_attribute *attr, const char *buf, size_t count)
+{
+	unsigned long num;
+	if (strict_strtoul(buf, 0, &num))
+		return -EINVAL;
+	if (num < 1 || num >= 100)
+		return -EINVAL;
+	mutex_lock(&isolated_cpus_lock);
+	idle_pct = num;
+	mutex_unlock(&isolated_cpus_lock);
+	return count;
+}
+
+static ssize_t acpi_pad_idlepct_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	return scnprintf(buf, PAGE_SIZE, "%d", idle_pct);
+}
+static DEVICE_ATTR(idlepct, S_IRUGO|S_IWUSR,
+	acpi_pad_idlepct_show,
+	acpi_pad_idlepct_store);
+
+static ssize_t acpi_pad_idlecpus_store(struct device *dev,
+	struct device_attribute *attr, const char *buf, size_t count)
+{
+	unsigned long num;
+	if (strict_strtoul(buf, 0, &num))
+		return -EINVAL;
+	mutex_lock(&isolated_cpus_lock);
+	acpi_pad_idle_cpus(num);
+	mutex_unlock(&isolated_cpus_lock);
+	return count;
+}
+
+static ssize_t acpi_pad_idlecpus_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	return cpumask_scnprintf(buf, PAGE_SIZE,
+		to_cpumask(pad_busy_cpus_bits));
+}
+static DEVICE_ATTR(idlecpus, S_IRUGO|S_IWUSR,
+	acpi_pad_idlecpus_show,
+	acpi_pad_idlecpus_store);
+
+static int acpi_pad_add_sysfs(struct acpi_device *device)
+{
+	int result;
+
+	result = device_create_file(&device->dev, &dev_attr_idlecpus);
+	if (result)
+		return -ENODEV;
+	result = device_create_file(&device->dev, &dev_attr_idlepct);
+	if (result) {
+		device_remove_file(&device->dev, &dev_attr_idlecpus);
+		return -ENODEV;
+	}
+	result = device_create_file(&device->dev, &dev_attr_rrtime);
+	if (result) {
+		device_remove_file(&device->dev, &dev_attr_idlecpus);
+		device_remove_file(&device->dev, &dev_attr_idlepct);
+		return -ENODEV;
+	}
+	return 0;
+}
+
+static void acpi_pad_remove_sysfs(struct acpi_device *device)
+{
+	device_remove_file(&device->dev, &dev_attr_idlecpus);
+	device_remove_file(&device->dev, &dev_attr_idlepct);
+	device_remove_file(&device->dev, &dev_attr_rrtime);
+}
+
+/* Query firmware how many CPUs should be idle */
+static int acpi_pad_pur(acpi_handle handle, int *num_cpus)
+{
+	struct acpi_buffer buffer = {ACPI_ALLOCATE_BUFFER, NULL};
+	acpi_status status;
+	union acpi_object *package;
+	int rev, num, ret = -EINVAL;
+
+	status = acpi_evaluate_object(handle, "_PUR", NULL, &buffer);
+	if (ACPI_FAILURE(status))
+		return -EINVAL;
+	package = buffer.pointer;
+	if (package->type != ACPI_TYPE_PACKAGE || package->package.count != 2)
+		goto out;
+	rev = package->package.elements[0].integer.value;
+	num = package->package.elements[1].integer.value;
+	if (rev != 1)
+		goto out;
+	*num_cpus = num;
+	ret = 0;
+out:
+	kfree(buffer.pointer);
+	return ret;
+}
+
+/* Notify firmware how many CPUs are idle */
+static void acpi_pad_ost(acpi_handle handle, int stat,
+	uint32_t idle_cpus)
+{
+	union acpi_object params[3] = {
+		{.type = ACPI_TYPE_INTEGER,},
+		{.type = ACPI_TYPE_INTEGER,},
+		{.type = ACPI_TYPE_BUFFER,},
+	};
+	struct acpi_object_list arg_list = {3, params};
+
+	params[0].integer.value = ACPI_PROCESSOR_AGGREGATOR_NOTIFY;
+	params[1].integer.value =  stat;
+	params[2].buffer.length = 4;
+	params[2].buffer.pointer = (void *)&idle_cpus;
+	acpi_evaluate_object(handle, "_OST", &arg_list, NULL);
+}
+
+static void acpi_pad_handle_notify(acpi_handle handle)
+{
+	int num_cpus, ret;
+	uint32_t idle_cpus;
+
+	mutex_lock(&isolated_cpus_lock);
+	if (acpi_pad_pur(handle, &num_cpus)) {
+		mutex_unlock(&isolated_cpus_lock);
+		return;
+	}
+	ret = acpi_pad_idle_cpus(num_cpus);
+	idle_cpus = acpi_pad_idle_cpus_num();
+	if (!ret)
+		acpi_pad_ost(handle, 0, idle_cpus);
+	else
+		acpi_pad_ost(handle, 1, 0);
+	mutex_unlock(&isolated_cpus_lock);
+}
+
+static void acpi_pad_notify(acpi_handle handle, u32 event,
+	void *data)
+{
+	struct acpi_device *device = data;
+
+	switch (event) {
+	case ACPI_PROCESSOR_AGGREGATOR_NOTIFY:
+		acpi_pad_handle_notify(handle);
+		acpi_bus_generate_proc_event(device, event, 0);
+		acpi_bus_generate_netlink_event(device->pnp.device_class,
+			dev_name(&device->dev), event, 0);
+		break;
+	default:
+		printk(KERN_WARNING"Unsupported event [0x%x]\n", event);
+		break;
+	}
+}
+
+static int acpi_pad_add(struct acpi_device *device)
+{
+	acpi_status status;
+
+	strcpy(acpi_device_name(device), ACPI_PROCESSOR_AGGREGATOR_DEVICE_NAME);
+	strcpy(acpi_device_class(device), ACPI_PROCESSOR_AGGREGATOR_CLASS);
+
+	if (acpi_pad_add_sysfs(device))
+		return -ENODEV;
+
+	status = acpi_install_notify_handler(device->handle,
+		ACPI_DEVICE_NOTIFY, acpi_pad_notify, device);
+	if (ACPI_FAILURE(status)) {
+		acpi_pad_remove_sysfs(device);
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+static int acpi_pad_remove(struct acpi_device *device,
+	int type)
+{
+	mutex_lock(&isolated_cpus_lock);
+	acpi_pad_idle_cpus(0);
+	mutex_unlock(&isolated_cpus_lock);
+
+	acpi_remove_notify_handler(device->handle,
+		ACPI_DEVICE_NOTIFY, acpi_pad_notify);
+	acpi_pad_remove_sysfs(device);
+	return 0;
+}
+
+static const struct acpi_device_id pad_device_ids[] = {
+	{"ACPI000C", 0},
+	{"", 0},
+};
+MODULE_DEVICE_TABLE(acpi, pad_device_ids);
+
+static struct acpi_driver acpi_pad_driver = {
+	.name = "processor_aggregator",
+	.class = ACPI_PROCESSOR_AGGREGATOR_CLASS,
+	.ids = pad_device_ids,
+	.ops = {
+		.add = acpi_pad_add,
+		.remove = acpi_pad_remove,
+	},
+};
+
+static int __init acpi_pad_init(void)
+{
+	power_saving_mwait_init();
+	if (power_saving_mwait_eax == 0)
+		return -EINVAL;
+
+	return acpi_bus_register_driver(&acpi_pad_driver);
+}
+
+static void __exit acpi_pad_exit(void)
+{
+	acpi_bus_unregister_driver(&acpi_pad_driver);
+}
+
+module_init(acpi_pad_init);
+module_exit(acpi_pad_exit);
+MODULE_AUTHOR("Shaohua Li<shaohua.li@intel.com>");
+MODULE_DESCRIPTION("ACPI Processor Aggregator Driver");
+MODULE_LICENSE("GPL");