Merge branch 'iks' of git://git.linaro.org/people/nico/linux into lsk-v3.10-ikstopic/v3.10/iks

11 files changed, 1099 insertions, 3 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 136f263ed47..61746a2f441 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1521,6 +1521,31 @@ config MCPM
 	  for (multi-)cluster based systems, such as big.LITTLE based
 	  systems.
 
+config BIG_LITTLE
+	bool "big.LITTLE support (Experimental)"
+	depends on CPU_V7 && SMP
+	select MCPM
+	help
+	  This option enables support for the big.LITTLE architecture.
+
+config BL_SWITCHER
+	bool "big.LITTLE switcher support"
+	depends on BIG_LITTLE && MCPM && HOTPLUG_CPU
+	select CPU_PM
+	select ARM_CPU_SUSPEND
+	help
+	  The big.LITTLE "switcher" provides the core functionality to
+	  transparently handle transition between a cluster of A15's
+	  and a cluster of A7's in a big.LITTLE system.
+
+config BL_SWITCHER_DUMMY_IF
+	tristate "Simple big.LITTLE switcher user interface"
+	depends on BL_SWITCHER && DEBUG_KERNEL
+	help
+	  This is a simple and dummy char dev interface to control
+	  the big.LITTLE switcher core code.  It is meant for
+	  debugging purposes only.
+
 choice
 	prompt "Memory split"
 	default VMSPLIT_3G
diff --git a/arch/arm/common/Makefile b/arch/arm/common/Makefile
index 48434cbe3e8..6073ffb8906 100644
--- a/arch/arm/common/Makefile
+++ b/arch/arm/common/Makefile
@@ -16,3 +16,5 @@ obj-$(CONFIG_ARM_TIMER_SP804)	+= timer-sp.o
 obj-$(CONFIG_MCPM)		+= mcpm_head.o mcpm_entry.o mcpm_platsmp.o vlock.o
 AFLAGS_mcpm_head.o		:= -march=armv7-a
 AFLAGS_vlock.o			:= -march=armv7-a
+obj-$(CONFIG_BL_SWITCHER)	+= bL_switcher.o
+obj-$(CONFIG_BL_SWITCHER_DUMMY_IF) += bL_switcher_dummy_if.o
diff --git a/arch/arm/common/bL_switcher.c b/arch/arm/common/bL_switcher.c
new file mode 100644
index 00000000000..1883c5b3e3f
--- /dev/null
+++ b/arch/arm/common/bL_switcher.c
@@ -0,0 +1,860 @@
+/*
+ * arch/arm/common/bL_switcher.c -- big.LITTLE cluster switcher core driver
+ *
+ * Created by:	Nicolas Pitre, March 2012
+ * Copyright:	(C) 2012  Linaro Limited
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/atomic.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/interrupt.h>
+#include <linux/cpu_pm.h>
+#include <linux/cpu.h>
+#include <linux/cpumask.h>
+#include <linux/kthread.h>
+#include <linux/wait.h>
+#include <linux/time.h>
+#include <linux/clockchips.h>
+#include <linux/hrtimer.h>
+#include <linux/tick.h>
+#include <linux/notifier.h>
+#include <linux/mm.h>
+#include <linux/mutex.h>
+#include <linux/smp.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+#include <linux/sysfs.h>
+#include <linux/irqchip/arm-gic.h>
+#include <linux/moduleparam.h>
+
+#include <asm/smp_plat.h>
+#include <asm/cacheflush.h>
+#include <asm/cputype.h>
+#include <asm/suspend.h>
+#include <asm/mcpm.h>
+#include <asm/bL_switcher.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/power_cpu_migrate.h>
+
+
+/*
+ * Use our own MPIDR accessors as the generic ones in asm/cputype.h have
+ * __attribute_const__ and we don't want the compiler to assume any
+ * constness here as the value _does_ change along some code paths.
+ */
+
+static int read_mpidr(void)
+{
+	unsigned int id;
+	asm volatile ("mrc\tp15, 0, %0, c0, c0, 5" : "=r" (id));
+	return id & MPIDR_HWID_BITMASK;
+}
+
+/*
+ * Get a global nanosecond time stamp for tracing.
+ */
+static s64 get_ns(void)
+{
+	struct timespec ts;
+	getnstimeofday(&ts);
+	return timespec_to_ns(&ts);
+}
+
+/*
+ * bL switcher core code.
+ */
+
+static void bL_do_switch(void *_arg)
+{
+	unsigned ib_mpidr, ib_cpu, ib_cluster;
+	long volatile handshake, **handshake_ptr = _arg;
+
+	pr_debug("%s\n", __func__);
+
+	ib_mpidr = cpu_logical_map(smp_processor_id());
+	ib_cpu = MPIDR_AFFINITY_LEVEL(ib_mpidr, 0);
+	ib_cluster = MPIDR_AFFINITY_LEVEL(ib_mpidr, 1);
+
+	/* Advertise our handshake location */
+	if (handshake_ptr) {
+		handshake = 0;
+		*handshake_ptr = &handshake;
+	} else
+		handshake = -1;
+
+	/*
+	 * Our state has been saved at this point.  Let's release our
+	 * inbound CPU.
+	 */
+	mcpm_set_entry_vector(ib_cpu, ib_cluster, cpu_resume);
+	sev();
+
+	/*
+	 * From this point, we must assume that our counterpart CPU might
+	 * have taken over in its parallel world already, as if execution
+	 * just returned from cpu_suspend().  It is therefore important to
+	 * be very careful not to make any change the other guy is not
+	 * expecting.  This is why we need stack isolation.
+	 *
+	 * Fancy under cover tasks could be performed here.  For now
+	 * we have none.
+	 */
+
+	/*
+	 * Let's wait until our inbound is alive.
+	 */
+	while (!handshake) {
+		wfe();
+		smp_mb();
+	}
+
+	/* Let's put ourself down. */
+	mcpm_cpu_power_down();
+
+	/* should never get here */
+	BUG();
+}
+
+/*
+ * Stack isolation.  To ensure 'current' remains valid, we just use another
+ * piece of our thread's stack space which should be fairly lightly used.
+ * The selected area starts just above the thread_info structure located
+ * at the very bottom of the stack, aligned to a cache line, and indexed
+ * with the cluster number.
+ */
+#define STACK_SIZE 512
+extern void call_with_stack(void (*fn)(void *), void *arg, void *sp);
+static int bL_switchpoint(unsigned long _arg)
+{
+	unsigned int mpidr = read_mpidr();
+	unsigned int clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
+	void *stack = current_thread_info() + 1;
+	stack = PTR_ALIGN(stack, L1_CACHE_BYTES);
+	stack += clusterid * STACK_SIZE + STACK_SIZE;
+	call_with_stack(bL_do_switch, (void *)_arg, stack);
+	BUG();
+}
+
+/*
+ * Generic switcher interface
+ */
+
+static unsigned int bL_gic_id[MAX_CPUS_PER_CLUSTER][MAX_NR_CLUSTERS];
+static int bL_switcher_cpu_pairing[NR_CPUS];
+
+/*
+ * bL_switch_to - Switch to a specific cluster for the current CPU
+ * @new_cluster_id: the ID of the cluster to switch to.
+ *
+ * This function must be called on the CPU to be switched.
+ * Returns 0 on success, else a negative status code.
+ */
+static int bL_switch_to(unsigned int new_cluster_id)
+{
+	unsigned int mpidr, this_cpu, that_cpu;
+	unsigned int ob_mpidr, ob_cpu, ob_cluster, ib_mpidr, ib_cpu, ib_cluster;
+	struct completion inbound_alive;
+	struct tick_device *tdev;
+	enum clock_event_mode tdev_mode;
+	long volatile *handshake_ptr;
+	int ipi_nr, ret;
+
+	this_cpu = smp_processor_id();
+	ob_mpidr = read_mpidr();
+	ob_cpu = MPIDR_AFFINITY_LEVEL(ob_mpidr, 0);
+	ob_cluster = MPIDR_AFFINITY_LEVEL(ob_mpidr, 1);
+	BUG_ON(cpu_logical_map(this_cpu) != ob_mpidr);
+
+	if (new_cluster_id == ob_cluster)
+		return 0;
+
+	that_cpu = bL_switcher_cpu_pairing[this_cpu];
+	ib_mpidr = cpu_logical_map(that_cpu);
+	ib_cpu = MPIDR_AFFINITY_LEVEL(ib_mpidr, 0);
+	ib_cluster = MPIDR_AFFINITY_LEVEL(ib_mpidr, 1);
+
+	pr_debug("before switch: CPU %d MPIDR %#x -> %#x\n",
+		 this_cpu, ob_mpidr, ib_mpidr);
+
+	this_cpu = smp_processor_id();
+
+	/* Close the gate for our entry vectors */
+	mcpm_set_entry_vector(ob_cpu, ob_cluster, NULL);
+	mcpm_set_entry_vector(ib_cpu, ib_cluster, NULL);
+
+	/* Install our "inbound alive" notifier. */
+	init_completion(&inbound_alive);
+	ipi_nr = register_ipi_completion(&inbound_alive, this_cpu);
+	ipi_nr |= ((1 << 16) << bL_gic_id[ob_cpu][ob_cluster]);
+	mcpm_set_early_poke(ib_cpu, ib_cluster, gic_get_sgir_physaddr(), ipi_nr);
+
+	/*
+	 * Let's wake up the inbound CPU now in case it requires some delay
+	 * to come online, but leave it gated in our entry vector code.
+	 */
+	ret = mcpm_cpu_power_up(ib_cpu, ib_cluster);
+	if (ret) {
+		pr_err("%s: mcpm_cpu_power_up() returned %d\n", __func__, ret);
+		return ret;
+	}
+
+	/*
+	 * Raise a SGI on the inbound CPU to make sure it doesn't stall
+	 * in a possible WFI, such as in bL_power_down().
+	 */
+	gic_send_sgi(bL_gic_id[ib_cpu][ib_cluster], 0);
+
+	/*
+	 * Wait for the inbound to come up.  This allows for other
+	 * tasks to be scheduled in the mean time.
+	 */
+	wait_for_completion(&inbound_alive);
+	mcpm_set_early_poke(ib_cpu, ib_cluster, 0, 0);
+
+	/*
+	 * From this point we are entering the switch critical zone
+	 * and can't sleep/schedule anymore.
+	 */
+	local_irq_disable();
+	local_fiq_disable();
+	trace_cpu_migrate_begin(get_ns(), ob_mpidr);
+
+	/* redirect GIC's SGIs to our counterpart */
+	gic_migrate_target(bL_gic_id[ib_cpu][ib_cluster]);
+
+	tdev = tick_get_device(this_cpu);
+	if (tdev && !cpumask_equal(tdev->evtdev->cpumask, cpumask_of(this_cpu)))
+		tdev = NULL;
+	if (tdev) {
+		tdev_mode = tdev->evtdev->mode;
+		clockevents_set_mode(tdev->evtdev, CLOCK_EVT_MODE_SHUTDOWN);
+	}
+
+	ret = cpu_pm_enter();
+
+	/* we can not tolerate errors at this point */
+	if (ret)
+		panic("%s: cpu_pm_enter() returned %d\n", __func__, ret);
+
+	/*
+	 * Swap the physical CPUs in the logical map for this logical CPU.
+	 * This must be flushed to RAM as the resume code
+	 * needs to access it while the caches are still disabled.
+	 */
+	cpu_logical_map(this_cpu) = ib_mpidr;
+	cpu_logical_map(that_cpu) = ob_mpidr;
+	sync_cache_w(&cpu_logical_map(this_cpu));
+
+	/* Let's do the actual CPU switch. */
+	ret = cpu_suspend((unsigned long)&handshake_ptr, bL_switchpoint);
+	if (ret > 0)
+		panic("%s: cpu_suspend() returned %d\n", __func__, ret);
+
+	/* We are executing on the inbound CPU at this point */
+	mpidr = read_mpidr();
+	pr_debug("after switch: CPU %d MPIDR %#x\n", this_cpu, mpidr);
+	BUG_ON(mpidr != ib_mpidr);
+
+	mcpm_cpu_powered_up();
+
+	ret = cpu_pm_exit();
+
+	if (tdev) {
+		clockevents_set_mode(tdev->evtdev, tdev_mode);
+		clockevents_program_event(tdev->evtdev,
+					  tdev->evtdev->next_event, 1);
+	}
+
+	trace_cpu_migrate_finish(get_ns(), ib_mpidr);
+	local_fiq_enable();
+	local_irq_enable();
+
+	*handshake_ptr = 1;
+	dsb_sev();
+
+	if (ret)
+		pr_err("%s exiting with error %d\n", __func__, ret);
+	return ret;
+}
+
+struct bL_thread {
+	spinlock_t lock;
+	struct task_struct *task;
+	wait_queue_head_t wq;
+	int wanted_cluster;
+	struct completion started;
+	bL_switch_completion_handler completer;
+	void *completer_cookie;
+};
+
+static struct bL_thread bL_threads[NR_CPUS];
+
+static int bL_switcher_thread(void *arg)
+{
+	struct bL_thread *t = arg;
+	struct sched_param param = { .sched_priority = 1 };
+	int cluster;
+	bL_switch_completion_handler completer;
+	void *completer_cookie;
+
+	sched_setscheduler_nocheck(current, SCHED_FIFO, &param);
+	complete(&t->started);
+
+	do {
+		if (signal_pending(current))
+			flush_signals(current);
+		wait_event_interruptible(t->wq,
+				t->wanted_cluster != -1 ||
+				kthread_should_stop());
+
+		spin_lock(&t->lock);
+		cluster = t->wanted_cluster;
+		completer = t->completer;
+		completer_cookie = t->completer_cookie;
+		t->wanted_cluster = -1;
+		t->completer = NULL;
+		spin_unlock(&t->lock);
+
+		if (cluster != -1) {
+			bL_switch_to(cluster);
+
+			if (completer)
+				completer(completer_cookie);
+		}
+	} while (!kthread_should_stop());
+
+	return 0;
+}
+
+static struct task_struct * bL_switcher_thread_create(int cpu, void *arg)
+{
+	struct task_struct *task;
+
+	task = kthread_create_on_node(bL_switcher_thread, arg,
+				      cpu_to_node(cpu), "kswitcher_%d", cpu);
+	if (!IS_ERR(task)) {
+		kthread_bind(task, cpu);
+		wake_up_process(task);
+	} else
+		pr_err("%s failed for CPU %d\n", __func__, cpu);
+	return task;
+}
+
+/*
+ * bL_switch_request_cb - Switch to a specific cluster for the given CPU,
+ *      with completion notification via a callback
+ *
+ * @cpu: the CPU to switch
+ * @new_cluster_id: the ID of the cluster to switch to.
+ * @completer: switch completion callback.  if non-NULL,
+ *	@completer(@completer_cookie) will be called on completion of
+ *	the switch, in non-atomic context.
+ * @completer_cookie: opaque context argument for @completer.
+ *
+ * This function causes a cluster switch on the given CPU by waking up
+ * the appropriate switcher thread.  This function may or may not return
+ * before the switch has occurred.
+ *
+ * If a @completer callback function is supplied, it will be called when
+ * the switch is complete.  This can be used to determine asynchronously
+ * when the switch is complete, regardless of when bL_switch_request()
+ * returns.  When @completer is supplied, no new switch request is permitted
+ * for the affected CPU until after the switch is complete, and @completer
+ * has returned.
+ */
+int bL_switch_request_cb(unsigned int cpu, unsigned int new_cluster_id,
+			 bL_switch_completion_handler completer,
+			 void *completer_cookie)
+{
+	struct bL_thread *t;
+
+	if (cpu >= ARRAY_SIZE(bL_threads)) {
+		pr_err("%s: cpu %d out of bounds\n", __func__, cpu);
+		return -EINVAL;
+	}
+
+	t = &bL_threads[cpu];
+
+	if (IS_ERR(t->task))
+		return PTR_ERR(t->task);
+	if (!t->task)
+		return -ESRCH;
+
+	spin_lock(&t->lock);
+	if (t->completer) {
+		spin_unlock(&t->lock);
+		return -EBUSY;
+	}
+	t->completer = completer;
+	t->completer_cookie = completer_cookie;
+	t->wanted_cluster = new_cluster_id;
+	spin_unlock(&t->lock);
+	wake_up(&t->wq);
+	return 0;
+}
+
+EXPORT_SYMBOL_GPL(bL_switch_request_cb);
+
+/*
+ * Detach an outstanding switch request.
+ *
+ * The switcher will continue with the switch request in the background,
+ * but the completer function will not be called.
+ *
+ * This may be necessary if the completer is in a kernel module which is
+ * about to be unloaded.
+ */
+void bL_switch_request_detach(unsigned int cpu,
+			      bL_switch_completion_handler completer)
+{
+	struct bL_thread *t;
+
+	if (cpu >= ARRAY_SIZE(bL_threads)) {
+		pr_err("%s: cpu %d out of bounds\n", __func__, cpu);
+		return;
+	}
+
+	t = &bL_threads[cpu];
+
+	if (IS_ERR(t->task) || !t->task)
+		return;
+
+	spin_lock(&t->lock);
+	if (t->completer == completer)
+		t->completer = NULL;
+	spin_unlock(&t->lock);
+}
+
+EXPORT_SYMBOL_GPL(bL_switch_request_detach);
+
+/*
+ * Activation and configuration code.
+ */
+
+static DEFINE_MUTEX(bL_switcher_activation_lock);
+static BLOCKING_NOTIFIER_HEAD(bL_activation_notifier);
+static unsigned int bL_switcher_active;
+static unsigned int bL_switcher_cpu_original_cluster[NR_CPUS];
+static cpumask_t bL_switcher_removed_logical_cpus;
+
+int bL_switcher_register_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&bL_activation_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(bL_switcher_register_notifier);
+
+int bL_switcher_unregister_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&bL_activation_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(bL_switcher_unregister_notifier);
+
+static int bL_activation_notify(unsigned long val)
+{
+	int ret;
+       
+	ret = blocking_notifier_call_chain(&bL_activation_notifier, val, NULL);
+	if (ret & NOTIFY_STOP_MASK)
+		pr_err("%s: notifier chain failed with status 0x%x\n",
+			__func__, ret);
+	return notifier_to_errno(ret);
+}
+
+static void bL_switcher_restore_cpus(void)
+{
+	int i;
+
+	for_each_cpu(i, &bL_switcher_removed_logical_cpus)
+		cpu_up(i);
+}
+
+static int bL_switcher_halve_cpus(void)
+{
+	int i, j, cluster_0, gic_id, ret;
+	unsigned int cpu, cluster, mask;
+	cpumask_t available_cpus;
+
+	/* First pass to validate what we have */
+	mask = 0;
+	for_each_online_cpu(i) {
+		cpu = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 0);
+		cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 1);
+		if (cluster >= 2) {
+			pr_err("%s: only dual cluster systems are supported\n", __func__);
+			return -EINVAL;
+		}
+		if (WARN_ON(cpu >= MAX_CPUS_PER_CLUSTER))
+			return -EINVAL;
+		mask |= (1 << cluster);
+	}
+	if (mask != 3) {
+		pr_err("%s: no CPU pairing possible\n", __func__);
+		return -EINVAL;
+	}
+
+	/*
+	 * Now let's do the pairing.  We match each CPU with another CPU
+	 * from a different cluster.  To get a uniform scheduling behavior
+	 * without fiddling with CPU topology and compute capacity data,
+	 * we'll use logical CPUs initially belonging to the same cluster.
+	 */
+	memset(bL_switcher_cpu_pairing, -1, sizeof(bL_switcher_cpu_pairing));
+	cpumask_copy(&available_cpus, cpu_online_mask);
+	cluster_0 = -1;
+	for_each_cpu(i, &available_cpus) {
+		int match = -1;
+		cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 1);
+		if (cluster_0 == -1)
+			cluster_0 = cluster;
+		if (cluster != cluster_0)
+			continue;
+		cpumask_clear_cpu(i, &available_cpus);
+		for_each_cpu(j, &available_cpus) {
+			cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(j), 1);
+			/*
+			 * Let's remember the last match to create "odd"
+			 * pairing on purpose in order for other code not
+			 * to assume any relation between physical and
+			 * logical CPU numbers.
+			 */
+			if (cluster != cluster_0)
+				match = j;
+		}
+		if (match != -1) {
+			bL_switcher_cpu_pairing[i] = match;
+			cpumask_clear_cpu(match, &available_cpus);
+			pr_info("CPU%d paired with CPU%d\n", i, match);
+		}
+	}
+
+	/*
+	 * Now we disable the unwanted CPUs i.e. everything that has no
+	 * pairing information (that includes the pairing counterparts).
+	 */ 
+	cpumask_clear(&bL_switcher_removed_logical_cpus);
+	for_each_online_cpu(i) {
+		cpu = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 0);
+		cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 1);
+
+		/* Let's take note of the GIC ID for this CPU */
+		gic_id = gic_get_cpu_id(i);
+		if (gic_id < 0) {
+			pr_err("%s: bad GIC ID for CPU %d\n", __func__, i);
+			bL_switcher_restore_cpus();
+			return -EINVAL;
+		}
+		bL_gic_id[cpu][cluster] = gic_id;
+		pr_info("GIC ID for CPU %u cluster %u is %u\n",
+			cpu, cluster, gic_id);
+
+		if (bL_switcher_cpu_pairing[i] != -1) {
+			bL_switcher_cpu_original_cluster[i] = cluster;
+			continue;
+		}
+
+		ret = cpu_down(i);
+		if (ret) {
+			bL_switcher_restore_cpus();
+			return ret;
+		}
+		cpumask_set_cpu(i, &bL_switcher_removed_logical_cpus);
+	}
+
+	return 0;
+}
+
+/* Determine the logical CPU a given physical CPU is grouped on. */
+int bL_switcher_get_logical_index(u32 mpidr)
+{
+	int cpu;
+
+	if (!bL_switcher_active)
+		return -EUNATCH;
+
+	mpidr &= MPIDR_HWID_BITMASK;
+	for_each_online_cpu(cpu) {
+		int pairing = bL_switcher_cpu_pairing[cpu];
+		if (pairing == -1)
+			continue;
+		if ((mpidr == cpu_logical_map(cpu)) ||
+		    (mpidr == cpu_logical_map(pairing)))
+			return cpu;
+	}
+	return -EINVAL;
+}
+
+static void bL_switcher_trace_trigger_cpu(void *__always_unused info)
+{
+	trace_cpu_migrate_current(get_ns(), read_mpidr());
+}
+
+int bL_switcher_trace_trigger(void)
+{
+	int ret;
+
+	preempt_disable();
+
+	bL_switcher_trace_trigger_cpu(NULL);
+	ret = smp_call_function(bL_switcher_trace_trigger_cpu, NULL, true);
+
+	preempt_enable();
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(bL_switcher_trace_trigger);
+
+static int bL_switcher_enable(void)
+{
+	int cpu, ret;
+
+	mutex_lock(&bL_switcher_activation_lock);
+	cpu_hotplug_driver_lock();
+	if (bL_switcher_active) {
+		cpu_hotplug_driver_unlock();
+		mutex_unlock(&bL_switcher_activation_lock);
+		return 0;
+	}
+
+	pr_info("big.LITTLE switcher initializing\n");
+
+	ret = bL_activation_notify(BL_NOTIFY_PRE_ENABLE);
+	if (ret)
+		goto error;
+
+	ret = bL_switcher_halve_cpus();
+	if (ret)
+		goto error;
+
+	bL_switcher_trace_trigger();
+
+	for_each_online_cpu(cpu) {
+		struct bL_thread *t = &bL_threads[cpu];
+		spin_lock_init(&t->lock);
+		init_waitqueue_head(&t->wq);
+		init_completion(&t->started);
+		t->wanted_cluster = -1;
+		t->task = bL_switcher_thread_create(cpu, t);
+	}
+
+	bL_switcher_active = 1;
+	bL_activation_notify(BL_NOTIFY_POST_ENABLE);
+	pr_info("big.LITTLE switcher initialized\n");
+	goto out;
+
+error:
+	pr_warning("big.LITTLE switcher initialization failed\n");
+	bL_activation_notify(BL_NOTIFY_POST_DISABLE);
+
+out:
+	cpu_hotplug_driver_unlock();
+	mutex_unlock(&bL_switcher_activation_lock);
+	return ret;
+}
+
+#ifdef CONFIG_SYSFS
+
+static void bL_switcher_disable(void)
+{
+	unsigned int cpu, cluster;
+	struct bL_thread *t;
+	struct task_struct *task;
+
+	mutex_lock(&bL_switcher_activation_lock);
+	cpu_hotplug_driver_lock();
+
+	if (!bL_switcher_active)
+		goto out;
+
+	if (bL_activation_notify(BL_NOTIFY_PRE_DISABLE) != 0) {
+		bL_activation_notify(BL_NOTIFY_POST_ENABLE);
+		goto out;
+	}
+
+	bL_switcher_active = 0;
+
+	/*
+	 * To deactivate the switcher, we must shut down the switcher
+	 * threads to prevent any other requests from being accepted.
+	 * Then, if the final cluster for given logical CPU is not the
+	 * same as the original one, we'll recreate a switcher thread
+	 * just for the purpose of switching the CPU back without any
+	 * possibility for interference from external requests.
+	 */
+	for_each_online_cpu(cpu) {
+		t = &bL_threads[cpu];
+		task = t->task;
+		t->task = NULL;
+		if (!task || IS_ERR(task))
+			continue;
+		kthread_stop(task);
+		/* no more switch may happen on this CPU at this point */
+		cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(cpu), 1);
+		if (cluster == bL_switcher_cpu_original_cluster[cpu])
+			continue;
+		init_completion(&t->started);
+		t->wanted_cluster = bL_switcher_cpu_original_cluster[cpu];
+		task = bL_switcher_thread_create(cpu, t);
+		if (!IS_ERR(task)) {
+			wait_for_completion(&t->started);
+			kthread_stop(task);
+			cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(cpu), 1);
+			if (cluster == bL_switcher_cpu_original_cluster[cpu])
+				continue;
+		}
+		/* If execution gets here, we're in trouble. */
+		pr_crit("%s: unable to restore original cluster for CPU %d\n",
+			__func__, cpu);
+		pr_crit("%s: CPU %d can't be restored\n",
+			__func__, bL_switcher_cpu_pairing[cpu]);
+		cpumask_clear_cpu(bL_switcher_cpu_pairing[cpu],
+				  &bL_switcher_removed_logical_cpus);
+	}
+
+	bL_switcher_restore_cpus();
+	bL_switcher_trace_trigger();
+
+	bL_activation_notify(BL_NOTIFY_POST_DISABLE);
+
+out:
+	cpu_hotplug_driver_unlock();
+	mutex_unlock(&bL_switcher_activation_lock);
+}
+
+static ssize_t bL_switcher_active_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%u\n", bL_switcher_active);
+}
+
+static ssize_t bL_switcher_active_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	int ret;
+
+	switch (buf[0]) {
+	case '0':
+		bL_switcher_disable();
+		ret = 0;
+		break;
+	case '1':
+		ret = bL_switcher_enable();
+		break;
+	default:
+		ret = -EINVAL;
+	}
+
+	return (ret >= 0) ? count : ret;
+}
+
+static ssize_t bL_switcher_trace_trigger_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	int ret = bL_switcher_trace_trigger();
+
+	return ret ? ret : count;
+}
+
+static struct kobj_attribute bL_switcher_active_attr =
+	__ATTR(active, 0644, bL_switcher_active_show, bL_switcher_active_store);
+
+static struct kobj_attribute bL_switcher_trace_trigger_attr =
+	__ATTR(trace_trigger, 0200, NULL, bL_switcher_trace_trigger_store);
+
+static struct attribute *bL_switcher_attrs[] = {
+	&bL_switcher_active_attr.attr,
+	&bL_switcher_trace_trigger_attr.attr,
+	NULL,
+};
+
+static struct attribute_group bL_switcher_attr_group = {
+	.attrs = bL_switcher_attrs,
+};
+
+static struct kobject *bL_switcher_kobj;
+
+static int __init bL_switcher_sysfs_init(void)
+{
+	int ret;
+
+	bL_switcher_kobj = kobject_create_and_add("bL_switcher", kernel_kobj);
+	if (!bL_switcher_kobj)
+		return -ENOMEM;
+	ret = sysfs_create_group(bL_switcher_kobj, &bL_switcher_attr_group);
+	if (ret)
+		kobject_put(bL_switcher_kobj);
+	return ret;
+}
+
+#endif  /* CONFIG_SYSFS */
+
+bool bL_switcher_get_enabled(void)
+{
+	mutex_lock(&bL_switcher_activation_lock);
+
+	return bL_switcher_active;
+}
+EXPORT_SYMBOL_GPL(bL_switcher_get_enabled);
+
+void bL_switcher_put_enabled(void)
+{
+	mutex_unlock(&bL_switcher_activation_lock);
+}
+EXPORT_SYMBOL_GPL(bL_switcher_put_enabled);
+
+/*
+ * Veto any CPU hotplug operation while the switcher is active.
+ * We're just not ready to deal with that given the trickery involved.
+ */
+static int bL_switcher_hotplug_callback(struct notifier_block *nfb,
+					unsigned long action, void *hcpu)
+{
+	switch (action) {
+	case CPU_UP_PREPARE:
+	case CPU_DOWN_PREPARE:
+		if (bL_switcher_active)
+			return NOTIFY_BAD;
+	}
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block bL_switcher_hotplug_notifier =
+        { &bL_switcher_hotplug_callback, NULL, 0 };
+
+static bool no_bL_switcher;
+core_param(no_bL_switcher, no_bL_switcher, bool, 0644);
+
+static int __init bL_switcher_init(void)
+{
+	int ret;
+
+	if (MAX_NR_CLUSTERS != 2) {
+		pr_err("%s: only dual cluster systems are supported\n", __func__);
+		return -EINVAL;
+	}
+
+	register_cpu_notifier(&bL_switcher_hotplug_notifier);
+
+	if (!no_bL_switcher) {
+		ret = bL_switcher_enable();
+		if (ret)
+			return ret;
+	}
+
+#ifdef CONFIG_SYSFS
+	ret = bL_switcher_sysfs_init();
+	if (ret)
+		pr_err("%s: unable to create sysfs entry\n", __func__);
+#endif
+
+	return 0;
+}
+
+late_initcall(bL_switcher_init);
diff --git a/arch/arm/common/bL_switcher_dummy_if.c b/arch/arm/common/bL_switcher_dummy_if.c
new file mode 100644
index 00000000000..5e2dd197e72
--- /dev/null
+++ b/arch/arm/common/bL_switcher_dummy_if.c
@@ -0,0 +1,71 @@
+/*
+ * arch/arm/common/bL_switcher_dummy_if.c -- b.L switcher dummy interface
+ *
+ * Created by:	Nicolas Pitre, November 2012
+ * Copyright:	(C) 2012  Linaro Limited
+ *
+ * Dummy interface to user space for debugging purpose only.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/miscdevice.h>
+#include <asm/uaccess.h>
+#include <asm/bL_switcher.h>
+
+static ssize_t bL_switcher_write(struct file *file, const char __user *buf,
+			size_t len, loff_t *pos)
+{
+	unsigned char val[3];
+	unsigned int cpu, cluster;
+	int ret;
+
+	pr_debug("%s\n", __func__);
+
+	if (len < 3)
+		return -EINVAL;
+
+	if (copy_from_user(val, buf, 3))
+		return -EFAULT;
+
+	/* format: <cpu#>,<cluster#> */
+	if (val[0] < '0' || val[0] > '4' ||
+	    val[1] != ',' ||
+	    val[2] < '0' || val[2] > '1')
+		return -EINVAL;
+
+	cpu = val[0] - '0';
+	cluster = val[2] - '0';
+	ret = bL_switch_request(cpu, cluster);
+
+	return ret ? : len;
+}
+
+static const struct file_operations bL_switcher_fops = {
+	.write		= bL_switcher_write,
+	.owner	= THIS_MODULE,
+};
+
+static struct miscdevice bL_switcher_device = {
+        MISC_DYNAMIC_MINOR,
+        "b.L_switcher",
+        &bL_switcher_fops
+};
+
+static int __init bL_switcher_dummy_if_init(void)
+{
+	return misc_register(&bL_switcher_device);
+}
+
+static void __exit bL_switcher_dummy_if_exit(void)
+{
+	misc_deregister(&bL_switcher_device);
+}
+
+module_init(bL_switcher_dummy_if_init);
+module_exit(bL_switcher_dummy_if_exit);
diff --git a/arch/arm/common/mcpm_entry.c b/arch/arm/common/mcpm_entry.c
index 370236dd1a0..4a2b32fd53a 100644
--- a/arch/arm/common/mcpm_entry.c
+++ b/arch/arm/common/mcpm_entry.c
@@ -27,6 +27,18 @@ void mcpm_set_entry_vector(unsigned cpu, unsigned cluster, void *ptr)
 	sync_cache_w(&mcpm_entry_vectors[cluster][cpu]);
 }
 
+extern unsigned long mcpm_entry_early_pokes[MAX_NR_CLUSTERS][MAX_CPUS_PER_CLUSTER][2];
+
+void mcpm_set_early_poke(unsigned cpu, unsigned cluster,
+			 unsigned long poke_phys_addr, unsigned long poke_val)
+{
+	unsigned long *poke = &mcpm_entry_early_pokes[cluster][cpu][0];
+	poke[0] = poke_phys_addr;
+	poke[1] = poke_val;
+	__cpuc_flush_dcache_area((void *)poke, 8);
+	outer_clean_range(__pa(poke), __pa(poke + 2));
+}
+
 static const struct mcpm_platform_ops *platform_ops;
 
 int __init mcpm_platform_register(const struct mcpm_platform_ops *ops)
diff --git a/arch/arm/common/mcpm_head.S b/arch/arm/common/mcpm_head.S
index 8178705c4b2..057e9c5a9e1 100644
--- a/arch/arm/common/mcpm_head.S
+++ b/arch/arm/common/mcpm_head.S
@@ -71,12 +71,19 @@ ENTRY(mcpm_entry_point)
 	 * position independent way.
 	 */
 	adr	r5, 3f
-	ldmia	r5, {r6, r7, r8, r11}
+	ldmia	r5, {r0, r6, r7, r8, r11}
+	add	r0, r5, r0			@ r0 = mcpm_entry_early_pokes
 	add	r6, r5, r6			@ r6 = mcpm_entry_vectors
 	ldr	r7, [r5, r7]			@ r7 = mcpm_power_up_setup_phys
 	add	r8, r5, r8			@ r8 = mcpm_sync
 	add	r11, r5, r11			@ r11 = first_man_locks
 
+	@ Perform an early poke, if any
+	add	r0, r0, r4, lsl #3
+	ldmia	r0, {r0, r1}
+	teq	r0, #0
+	strne	r1, [r0]
+
 	mov	r0, #MCPM_SYNC_CLUSTER_SIZE
 	mla	r8, r0, r10, r8			@ r8 = sync cluster base
 
@@ -195,7 +202,8 @@ mcpm_entry_gated:
 
 	.align	2
 
-3:	.word	mcpm_entry_vectors - .
+3:	.word	mcpm_entry_early_pokes - .
+	.word	mcpm_entry_vectors - 3b
 	.word	mcpm_power_up_setup_phys - 3b
 	.word	mcpm_sync - 3b
 	.word	first_man_locks - 3b
@@ -214,6 +222,10 @@ first_man_locks:
 ENTRY(mcpm_entry_vectors)
 	.space	4 * MAX_NR_CLUSTERS * MAX_CPUS_PER_CLUSTER
 
+	.type	mcpm_entry_early_pokes, #object
+ENTRY(mcpm_entry_early_pokes)
+	.space	8 * MAX_NR_CLUSTERS * MAX_CPUS_PER_CLUSTER
+
 	.type	mcpm_power_up_setup_phys, #object
 ENTRY(mcpm_power_up_setup_phys)
 	.space  4		@ set by mcpm_sync_init()
diff --git a/arch/arm/include/asm/bL_switcher.h b/arch/arm/include/asm/bL_switcher.h
new file mode 100644
index 00000000000..482383b45c9
--- /dev/null
+++ b/arch/arm/include/asm/bL_switcher.h
@@ -0,0 +1,83 @@
+/*
+ * arch/arm/include/asm/bL_switcher.h
+ *
+ * Created by:  Nicolas Pitre, April 2012
+ * Copyright:   (C) 2012  Linaro Limited
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef ASM_BL_SWITCHER_H
+#define ASM_BL_SWITCHER_H
+
+#include <linux/compiler.h>
+#include <linux/types.h>
+
+typedef void (*bL_switch_completion_handler)(void *cookie);
+
+int bL_switch_request_cb(unsigned int cpu, unsigned int new_cluster_id,
+			 bL_switch_completion_handler completer,
+			 void *completer_cookie);
+static inline int bL_switch_request(unsigned int cpu, unsigned int new_cluster_id)
+{
+	return bL_switch_request_cb(cpu, new_cluster_id, NULL, NULL);
+}
+
+/*
+ * Register here to be notified about runtime enabling/disabling of
+ * the switcher.
+ *
+ * The notifier chain is called with the switcher activation lock held:
+ * the switcher will not be enabled or disabled during callbacks.
+ * Callbacks must not call bL_switcher_{get,put}_enabled().
+ */
+#define BL_NOTIFY_PRE_ENABLE	0
+#define BL_NOTIFY_POST_ENABLE	1
+#define BL_NOTIFY_PRE_DISABLE	2
+#define BL_NOTIFY_POST_DISABLE	3
+
+#ifdef CONFIG_BL_SWITCHER
+
+void bL_switch_request_detach(unsigned int cpu,
+			      bL_switch_completion_handler completer);
+
+int bL_switcher_register_notifier(struct notifier_block *nb);
+int bL_switcher_unregister_notifier(struct notifier_block *nb);
+
+/*
+ * Use these functions to temporarily prevent enabling/disabling of
+ * the switcher.
+ * bL_switcher_get_enabled() returns true if the switcher is currently
+ * enabled.  Each call to bL_switcher_get_enabled() must be followed
+ * by a call to bL_switcher_put_enabled().  These functions are not
+ * recursive.
+ */
+bool bL_switcher_get_enabled(void);
+void bL_switcher_put_enabled(void);
+
+int bL_switcher_trace_trigger(void);
+int bL_switcher_get_logical_index(u32 mpidr);
+
+#else
+static void bL_switch_request_detach(unsigned int cpu,
+				     bL_switch_completion_handler completer) { }
+
+static inline int bL_switcher_register_notifier(struct notifier_block *nb)
+{
+	return 0;
+}
+
+static inline int bL_switcher_unregister_notifier(struct notifier_block *nb)
+{
+	return 0;
+}
+
+static inline bool bL_switcher_get_enabled(void) { return false; }
+static inline void bL_switcher_put_enabled(void) { }
+static inline int bL_switcher_trace_trigger(void) { return 0; }
+static inline int bL_switcher_get_logical_index(u32 mpidr) { return -EUNATCH; }
+#endif /* CONFIG_BL_SWITCHER */
+
+#endif
diff --git a/arch/arm/include/asm/hardirq.h b/arch/arm/include/asm/hardirq.h
index 2740c2a2df6..3d7351c844a 100644
--- a/arch/arm/include/asm/hardirq.h
+++ b/arch/arm/include/asm/hardirq.h
@@ -5,7 +5,7 @@
 #include <linux/threads.h>
 #include <asm/irq.h>
 
-#define NR_IPI	6
+#define NR_IPI	7
 
 typedef struct {
 	unsigned int __softirq_pending;
diff --git a/arch/arm/include/asm/mcpm.h b/arch/arm/include/asm/mcpm.h
index 0f7b7620e9a..7626a7fd493 100644
--- a/arch/arm/include/asm/mcpm.h
+++ b/arch/arm/include/asm/mcpm.h
@@ -42,6 +42,14 @@ extern void mcpm_entry_point(void);
 void mcpm_set_entry_vector(unsigned cpu, unsigned cluster, void *ptr);
 
 /*
+ * This sets an early poke i.e a value to be poked into some address
+ * from very early assembly code before the CPU is ungated.  The
+ * address must be physical, and if 0 then nothing will happen.
+ */
+void mcpm_set_early_poke(unsigned cpu, unsigned cluster,
+			 unsigned long poke_phys_addr, unsigned long poke_val);
+
+/*
  * CPU/cluster power operations API for higher subsystems to use.
  */
 
diff --git a/arch/arm/include/asm/smp.h b/arch/arm/include/asm/smp.h
index d3a22bebe6c..610ccf33f5e 100644
--- a/arch/arm/include/asm/smp.h
+++ b/arch/arm/include/asm/smp.h
@@ -81,6 +81,8 @@ extern void arch_send_call_function_single_ipi(int cpu);
 extern void arch_send_call_function_ipi_mask(const struct cpumask *mask);
 extern void arch_send_wakeup_ipi_mask(const struct cpumask *mask);
 
+extern int register_ipi_completion(struct completion *completion, int cpu);
+
 struct smp_operations {
 #ifdef CONFIG_SMP
 	/*
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 5919eb451bb..dc05ca77963 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -66,6 +66,7 @@ enum ipi_msg_type {
 	IPI_CALL_FUNC,
 	IPI_CALL_FUNC_SINGLE,
 	IPI_CPU_STOP,
+	IPI_COMPLETION,
 };
 
 static DECLARE_COMPLETION(cpu_running);
@@ -463,6 +464,7 @@ static const char *ipi_types[NR_IPI] = {
 	S(IPI_CALL_FUNC, "Function call interrupts"),
 	S(IPI_CALL_FUNC_SINGLE, "Single function call interrupts"),
 	S(IPI_CPU_STOP, "CPU stop interrupts"),
+	S(IPI_COMPLETION, "completion interrupts"),
 };
 
 void show_ipi_list(struct seq_file *p, int prec)
@@ -588,6 +590,19 @@ static void ipi_cpu_stop(unsigned int cpu)
 		cpu_relax();
 }
 
+static DEFINE_PER_CPU(struct completion *, cpu_completion);
+
+int register_ipi_completion(struct completion *completion, int cpu)
+{
+	per_cpu(cpu_completion, cpu) = completion;
+	return IPI_COMPLETION;
+}
+
+static void ipi_complete(unsigned int cpu)
+{
+	complete(per_cpu(cpu_completion, cpu));
+}
+
 /*
  * Main handler for inter-processor interrupts
  */
@@ -638,6 +653,12 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
 		irq_exit();
 		break;
 
+	case IPI_COMPLETION:
+		irq_enter();
+		ipi_complete(cpu);
+		irq_exit();
+		break;
+
 	default:
 		printk(KERN_CRIT "CPU%u: Unknown IPI message 0x%x\n",
 		       cpu, ipinr);