2 * arch/arm/common/bL_switcher.c -- big.LITTLE cluster switcher core driver
4 * Created by: Nicolas Pitre, March 2012
5 * Copyright: (C) 2012-2013 Linaro Limited
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License version 2 as
9 * published by the Free Software Foundation.
12 #include <linux/atomic.h>
13 #include <linux/init.h>
14 #include <linux/kernel.h>
15 #include <linux/module.h>
16 #include <linux/sched.h>
17 #include <linux/interrupt.h>
18 #include <linux/cpu_pm.h>
19 #include <linux/cpu.h>
20 #include <linux/cpumask.h>
21 #include <linux/kthread.h>
22 #include <linux/wait.h>
23 #include <linux/time.h>
24 #include <linux/clockchips.h>
25 #include <linux/hrtimer.h>
26 #include <linux/tick.h>
27 #include <linux/notifier.h>
29 #include <linux/mutex.h>
30 #include <linux/spinlock.h>
31 #include <linux/string.h>
32 #include <linux/sysfs.h>
33 #include <linux/irqchip/arm-gic.h>
34 #include <linux/moduleparam.h>
36 #include <asm/smp_plat.h>
37 #include <asm/cputype.h>
38 #include <asm/suspend.h>
40 #include <asm/bL_switcher.h>
42 #define CREATE_TRACE_POINTS
43 #include <trace/events/power_cpu_migrate.h>
47 * Use our own MPIDR accessors as the generic ones in asm/cputype.h have
48 * __attribute_const__ and we don't want the compiler to assume any
49 * constness here as the value _does_ change along some code paths.
52 static int read_mpidr(void)
55 asm volatile ("mrc p15, 0, %0, c0, c0, 5" : "=r" (id));
56 return id & MPIDR_HWID_BITMASK;
60 * Get a global nanosecond time stamp for tracing.
62 static s64 get_ns(void)
66 return timespec_to_ns(&ts);
70 * bL switcher core code.
73 static void bL_do_switch(void *_arg)
75 unsigned ib_mpidr, ib_cpu, ib_cluster;
76 long volatile handshake, **handshake_ptr = _arg;
78 pr_debug("%s\n", __func__);
80 ib_mpidr = cpu_logical_map(smp_processor_id());
81 ib_cpu = MPIDR_AFFINITY_LEVEL(ib_mpidr, 0);
82 ib_cluster = MPIDR_AFFINITY_LEVEL(ib_mpidr, 1);
84 /* Advertise our handshake location */
87 *handshake_ptr = &handshake;
92 * Our state has been saved at this point. Let's release our
95 mcpm_set_entry_vector(ib_cpu, ib_cluster, cpu_resume);
99 * From this point, we must assume that our counterpart CPU might
100 * have taken over in its parallel world already, as if execution
101 * just returned from cpu_suspend(). It is therefore important to
102 * be very careful not to make any change the other guy is not
103 * expecting. This is why we need stack isolation.
105 * Fancy under cover tasks could be performed here. For now
110 * Let's wait until our inbound is alive.
117 /* Let's put ourself down. */
118 mcpm_cpu_power_down();
120 /* should never get here */
125 * Stack isolation. To ensure 'current' remains valid, we just use another
126 * piece of our thread's stack space which should be fairly lightly used.
127 * The selected area starts just above the thread_info structure located
128 * at the very bottom of the stack, aligned to a cache line, and indexed
129 * with the cluster number.
131 #define STACK_SIZE 512
132 extern void call_with_stack(void (*fn)(void *), void *arg, void *sp);
133 static int bL_switchpoint(unsigned long _arg)
135 unsigned int mpidr = read_mpidr();
136 unsigned int clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
137 void *stack = current_thread_info() + 1;
138 stack = PTR_ALIGN(stack, L1_CACHE_BYTES);
139 stack += clusterid * STACK_SIZE + STACK_SIZE;
140 call_with_stack(bL_do_switch, (void *)_arg, stack);
145 * Generic switcher interface
148 static unsigned int bL_gic_id[MAX_CPUS_PER_CLUSTER][MAX_NR_CLUSTERS];
149 static int bL_switcher_cpu_pairing[NR_CPUS];
152 * bL_switch_to - Switch to a specific cluster for the current CPU
153 * @new_cluster_id: the ID of the cluster to switch to.
155 * This function must be called on the CPU to be switched.
156 * Returns 0 on success, else a negative status code.
158 static int bL_switch_to(unsigned int new_cluster_id)
160 unsigned int mpidr, this_cpu, that_cpu;
161 unsigned int ob_mpidr, ob_cpu, ob_cluster, ib_mpidr, ib_cpu, ib_cluster;
162 struct completion inbound_alive;
163 struct tick_device *tdev;
164 enum clock_event_mode tdev_mode;
165 long volatile *handshake_ptr;
168 this_cpu = smp_processor_id();
169 ob_mpidr = read_mpidr();
170 ob_cpu = MPIDR_AFFINITY_LEVEL(ob_mpidr, 0);
171 ob_cluster = MPIDR_AFFINITY_LEVEL(ob_mpidr, 1);
172 BUG_ON(cpu_logical_map(this_cpu) != ob_mpidr);
174 if (new_cluster_id == ob_cluster)
177 that_cpu = bL_switcher_cpu_pairing[this_cpu];
178 ib_mpidr = cpu_logical_map(that_cpu);
179 ib_cpu = MPIDR_AFFINITY_LEVEL(ib_mpidr, 0);
180 ib_cluster = MPIDR_AFFINITY_LEVEL(ib_mpidr, 1);
182 pr_debug("before switch: CPU %d MPIDR %#x -> %#x\n",
183 this_cpu, ob_mpidr, ib_mpidr);
185 this_cpu = smp_processor_id();
187 /* Close the gate for our entry vectors */
188 mcpm_set_entry_vector(ob_cpu, ob_cluster, NULL);
189 mcpm_set_entry_vector(ib_cpu, ib_cluster, NULL);
191 /* Install our "inbound alive" notifier. */
192 init_completion(&inbound_alive);
193 ipi_nr = register_ipi_completion(&inbound_alive, this_cpu);
194 ipi_nr |= ((1 << 16) << bL_gic_id[ob_cpu][ob_cluster]);
195 mcpm_set_early_poke(ib_cpu, ib_cluster, gic_get_sgir_physaddr(), ipi_nr);
198 * Let's wake up the inbound CPU now in case it requires some delay
199 * to come online, but leave it gated in our entry vector code.
201 ret = mcpm_cpu_power_up(ib_cpu, ib_cluster);
203 pr_err("%s: mcpm_cpu_power_up() returned %d\n", __func__, ret);
208 * Raise a SGI on the inbound CPU to make sure it doesn't stall
209 * in a possible WFI, such as in bL_power_down().
211 gic_send_sgi(bL_gic_id[ib_cpu][ib_cluster], 0);
214 * Wait for the inbound to come up. This allows for other
215 * tasks to be scheduled in the mean time.
217 wait_for_completion(&inbound_alive);
218 mcpm_set_early_poke(ib_cpu, ib_cluster, 0, 0);
221 * From this point we are entering the switch critical zone
222 * and can't take any interrupts anymore.
226 trace_cpu_migrate_begin(get_ns(), ob_mpidr);
228 /* redirect GIC's SGIs to our counterpart */
229 gic_migrate_target(bL_gic_id[ib_cpu][ib_cluster]);
231 tdev = tick_get_device(this_cpu);
232 if (tdev && !cpumask_equal(tdev->evtdev->cpumask, cpumask_of(this_cpu)))
235 tdev_mode = tdev->evtdev->mode;
236 clockevents_set_mode(tdev->evtdev, CLOCK_EVT_MODE_SHUTDOWN);
239 ret = cpu_pm_enter();
241 /* we can not tolerate errors at this point */
243 panic("%s: cpu_pm_enter() returned %d\n", __func__, ret);
245 /* Swap the physical CPUs in the logical map for this logical CPU. */
246 cpu_logical_map(this_cpu) = ib_mpidr;
247 cpu_logical_map(that_cpu) = ob_mpidr;
249 /* Let's do the actual CPU switch. */
250 ret = cpu_suspend((unsigned long)&handshake_ptr, bL_switchpoint);
252 panic("%s: cpu_suspend() returned %d\n", __func__, ret);
254 /* We are executing on the inbound CPU at this point */
255 mpidr = read_mpidr();
256 pr_debug("after switch: CPU %d MPIDR %#x\n", this_cpu, mpidr);
257 BUG_ON(mpidr != ib_mpidr);
259 mcpm_cpu_powered_up();
264 clockevents_set_mode(tdev->evtdev, tdev_mode);
265 clockevents_program_event(tdev->evtdev,
266 tdev->evtdev->next_event, 1);
269 trace_cpu_migrate_finish(get_ns(), ib_mpidr);
277 pr_err("%s exiting with error %d\n", __func__, ret);
283 struct task_struct *task;
284 wait_queue_head_t wq;
286 struct completion started;
287 bL_switch_completion_handler completer;
288 void *completer_cookie;
291 static struct bL_thread bL_threads[NR_CPUS];
293 static int bL_switcher_thread(void *arg)
295 struct bL_thread *t = arg;
296 struct sched_param param = { .sched_priority = 1 };
298 bL_switch_completion_handler completer;
299 void *completer_cookie;
301 sched_setscheduler_nocheck(current, SCHED_FIFO, ¶m);
302 complete(&t->started);
305 if (signal_pending(current))
306 flush_signals(current);
307 wait_event_interruptible(t->wq,
308 t->wanted_cluster != -1 ||
309 kthread_should_stop());
312 cluster = t->wanted_cluster;
313 completer = t->completer;
314 completer_cookie = t->completer_cookie;
315 t->wanted_cluster = -1;
317 spin_unlock(&t->lock);
320 bL_switch_to(cluster);
323 completer(completer_cookie);
325 } while (!kthread_should_stop());
330 static struct task_struct *bL_switcher_thread_create(int cpu, void *arg)
332 struct task_struct *task;
334 task = kthread_create_on_node(bL_switcher_thread, arg,
335 cpu_to_node(cpu), "kswitcher_%d", cpu);
337 kthread_bind(task, cpu);
338 wake_up_process(task);
340 pr_err("%s failed for CPU %d\n", __func__, cpu);
345 * bL_switch_request_cb - Switch to a specific cluster for the given CPU,
346 * with completion notification via a callback
348 * @cpu: the CPU to switch
349 * @new_cluster_id: the ID of the cluster to switch to.
350 * @completer: switch completion callback. if non-NULL,
351 * @completer(@completer_cookie) will be called on completion of
352 * the switch, in non-atomic context.
353 * @completer_cookie: opaque context argument for @completer.
355 * This function causes a cluster switch on the given CPU by waking up
356 * the appropriate switcher thread. This function may or may not return
357 * before the switch has occurred.
359 * If a @completer callback function is supplied, it will be called when
360 * the switch is complete. This can be used to determine asynchronously
361 * when the switch is complete, regardless of when bL_switch_request()
362 * returns. When @completer is supplied, no new switch request is permitted
363 * for the affected CPU until after the switch is complete, and @completer
366 int bL_switch_request_cb(unsigned int cpu, unsigned int new_cluster_id,
367 bL_switch_completion_handler completer,
368 void *completer_cookie)
372 if (cpu >= ARRAY_SIZE(bL_threads)) {
373 pr_err("%s: cpu %d out of bounds\n", __func__, cpu);
377 t = &bL_threads[cpu];
380 return PTR_ERR(t->task);
386 spin_unlock(&t->lock);
389 t->completer = completer;
390 t->completer_cookie = completer_cookie;
391 t->wanted_cluster = new_cluster_id;
392 spin_unlock(&t->lock);
396 EXPORT_SYMBOL_GPL(bL_switch_request_cb);
399 * Activation and configuration code.
402 static DEFINE_MUTEX(bL_switcher_activation_lock);
403 static BLOCKING_NOTIFIER_HEAD(bL_activation_notifier);
404 static unsigned int bL_switcher_active;
405 static unsigned int bL_switcher_cpu_original_cluster[NR_CPUS];
406 static cpumask_t bL_switcher_removed_logical_cpus;
408 int bL_switcher_register_notifier(struct notifier_block *nb)
410 return blocking_notifier_chain_register(&bL_activation_notifier, nb);
412 EXPORT_SYMBOL_GPL(bL_switcher_register_notifier);
414 int bL_switcher_unregister_notifier(struct notifier_block *nb)
416 return blocking_notifier_chain_unregister(&bL_activation_notifier, nb);
418 EXPORT_SYMBOL_GPL(bL_switcher_unregister_notifier);
420 static int bL_activation_notify(unsigned long val)
424 ret = blocking_notifier_call_chain(&bL_activation_notifier, val, NULL);
425 if (ret & NOTIFY_STOP_MASK)
426 pr_err("%s: notifier chain failed with status 0x%x\n",
428 return notifier_to_errno(ret);
431 static void bL_switcher_restore_cpus(void)
435 for_each_cpu(i, &bL_switcher_removed_logical_cpus)
439 static int bL_switcher_halve_cpus(void)
441 int i, j, cluster_0, gic_id, ret;
442 unsigned int cpu, cluster, mask;
443 cpumask_t available_cpus;
445 /* First pass to validate what we have */
447 for_each_online_cpu(i) {
448 cpu = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 0);
449 cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 1);
451 pr_err("%s: only dual cluster systems are supported\n", __func__);
454 if (WARN_ON(cpu >= MAX_CPUS_PER_CLUSTER))
456 mask |= (1 << cluster);
459 pr_err("%s: no CPU pairing possible\n", __func__);
464 * Now let's do the pairing. We match each CPU with another CPU
465 * from a different cluster. To get a uniform scheduling behavior
466 * without fiddling with CPU topology and compute capacity data,
467 * we'll use logical CPUs initially belonging to the same cluster.
469 memset(bL_switcher_cpu_pairing, -1, sizeof(bL_switcher_cpu_pairing));
470 cpumask_copy(&available_cpus, cpu_online_mask);
472 for_each_cpu(i, &available_cpus) {
474 cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 1);
477 if (cluster != cluster_0)
479 cpumask_clear_cpu(i, &available_cpus);
480 for_each_cpu(j, &available_cpus) {
481 cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(j), 1);
483 * Let's remember the last match to create "odd"
484 * pairings on purpose in order for other code not
485 * to assume any relation between physical and
486 * logical CPU numbers.
488 if (cluster != cluster_0)
492 bL_switcher_cpu_pairing[i] = match;
493 cpumask_clear_cpu(match, &available_cpus);
494 pr_info("CPU%d paired with CPU%d\n", i, match);
499 * Now we disable the unwanted CPUs i.e. everything that has no
500 * pairing information (that includes the pairing counterparts).
502 cpumask_clear(&bL_switcher_removed_logical_cpus);
503 for_each_online_cpu(i) {
504 cpu = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 0);
505 cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 1);
507 /* Let's take note of the GIC ID for this CPU */
508 gic_id = gic_get_cpu_id(i);
510 pr_err("%s: bad GIC ID for CPU %d\n", __func__, i);
511 bL_switcher_restore_cpus();
514 bL_gic_id[cpu][cluster] = gic_id;
515 pr_info("GIC ID for CPU %u cluster %u is %u\n",
516 cpu, cluster, gic_id);
518 if (bL_switcher_cpu_pairing[i] != -1) {
519 bL_switcher_cpu_original_cluster[i] = cluster;
525 bL_switcher_restore_cpus();
528 cpumask_set_cpu(i, &bL_switcher_removed_logical_cpus);
534 static int bL_switcher_enable(void)
538 mutex_lock(&bL_switcher_activation_lock);
539 cpu_hotplug_driver_lock();
540 if (bL_switcher_active) {
541 cpu_hotplug_driver_unlock();
542 mutex_unlock(&bL_switcher_activation_lock);
546 pr_info("big.LITTLE switcher initializing\n");
548 ret = bL_activation_notify(BL_NOTIFY_PRE_ENABLE);
552 ret = bL_switcher_halve_cpus();
556 for_each_online_cpu(cpu) {
557 struct bL_thread *t = &bL_threads[cpu];
558 spin_lock_init(&t->lock);
559 init_waitqueue_head(&t->wq);
560 init_completion(&t->started);
561 t->wanted_cluster = -1;
562 t->task = bL_switcher_thread_create(cpu, t);
565 bL_switcher_active = 1;
566 bL_activation_notify(BL_NOTIFY_POST_ENABLE);
567 pr_info("big.LITTLE switcher initialized\n");
571 pr_warn("big.LITTLE switcher initialization failed\n");
572 bL_activation_notify(BL_NOTIFY_POST_DISABLE);
575 cpu_hotplug_driver_unlock();
576 mutex_unlock(&bL_switcher_activation_lock);
582 static void bL_switcher_disable(void)
584 unsigned int cpu, cluster;
586 struct task_struct *task;
588 mutex_lock(&bL_switcher_activation_lock);
589 cpu_hotplug_driver_lock();
591 if (!bL_switcher_active)
594 if (bL_activation_notify(BL_NOTIFY_PRE_DISABLE) != 0) {
595 bL_activation_notify(BL_NOTIFY_POST_ENABLE);
599 bL_switcher_active = 0;
602 * To deactivate the switcher, we must shut down the switcher
603 * threads to prevent any other requests from being accepted.
604 * Then, if the final cluster for given logical CPU is not the
605 * same as the original one, we'll recreate a switcher thread
606 * just for the purpose of switching the CPU back without any
607 * possibility for interference from external requests.
609 for_each_online_cpu(cpu) {
610 t = &bL_threads[cpu];
613 if (!task || IS_ERR(task))
616 /* no more switch may happen on this CPU at this point */
617 cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(cpu), 1);
618 if (cluster == bL_switcher_cpu_original_cluster[cpu])
620 init_completion(&t->started);
621 t->wanted_cluster = bL_switcher_cpu_original_cluster[cpu];
622 task = bL_switcher_thread_create(cpu, t);
624 wait_for_completion(&t->started);
626 cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(cpu), 1);
627 if (cluster == bL_switcher_cpu_original_cluster[cpu])
630 /* If execution gets here, we're in trouble. */
631 pr_crit("%s: unable to restore original cluster for CPU %d\n",
633 pr_crit("%s: CPU %d can't be restored\n",
634 __func__, bL_switcher_cpu_pairing[cpu]);
635 cpumask_clear_cpu(bL_switcher_cpu_pairing[cpu],
636 &bL_switcher_removed_logical_cpus);
639 bL_switcher_restore_cpus();
640 bL_activation_notify(BL_NOTIFY_POST_DISABLE);
643 cpu_hotplug_driver_unlock();
644 mutex_unlock(&bL_switcher_activation_lock);
647 static ssize_t bL_switcher_active_show(struct kobject *kobj,
648 struct kobj_attribute *attr, char *buf)
650 return sprintf(buf, "%u\n", bL_switcher_active);
653 static ssize_t bL_switcher_active_store(struct kobject *kobj,
654 struct kobj_attribute *attr, const char *buf, size_t count)
660 bL_switcher_disable();
664 ret = bL_switcher_enable();
670 return (ret >= 0) ? count : ret;
673 static struct kobj_attribute bL_switcher_active_attr =
674 __ATTR(active, 0644, bL_switcher_active_show, bL_switcher_active_store);
676 static struct attribute *bL_switcher_attrs[] = {
677 &bL_switcher_active_attr.attr,
681 static struct attribute_group bL_switcher_attr_group = {
682 .attrs = bL_switcher_attrs,
685 static struct kobject *bL_switcher_kobj;
687 static int __init bL_switcher_sysfs_init(void)
691 bL_switcher_kobj = kobject_create_and_add("bL_switcher", kernel_kobj);
692 if (!bL_switcher_kobj)
694 ret = sysfs_create_group(bL_switcher_kobj, &bL_switcher_attr_group);
696 kobject_put(bL_switcher_kobj);
700 #endif /* CONFIG_SYSFS */
702 bool bL_switcher_get_enabled(void)
704 mutex_lock(&bL_switcher_activation_lock);
706 return bL_switcher_active;
708 EXPORT_SYMBOL_GPL(bL_switcher_get_enabled);
710 void bL_switcher_put_enabled(void)
712 mutex_unlock(&bL_switcher_activation_lock);
714 EXPORT_SYMBOL_GPL(bL_switcher_put_enabled);
717 * Veto any CPU hotplug operation on those CPUs we've removed
718 * while the switcher is active.
719 * We're just not ready to deal with that given the trickery involved.
721 static int bL_switcher_hotplug_callback(struct notifier_block *nfb,
722 unsigned long action, void *hcpu)
724 if (bL_switcher_active) {
725 int pairing = bL_switcher_cpu_pairing[(unsigned long)hcpu];
726 switch (action & 0xf) {
728 case CPU_DOWN_PREPARE:
736 static bool no_bL_switcher;
737 core_param(no_bL_switcher, no_bL_switcher, bool, 0644);
739 static int __init bL_switcher_init(void)
743 if (MAX_NR_CLUSTERS != 2) {
744 pr_err("%s: only dual cluster systems are supported\n", __func__);
748 cpu_notifier(bL_switcher_hotplug_callback, 0);
750 if (!no_bL_switcher) {
751 ret = bL_switcher_enable();
757 ret = bL_switcher_sysfs_init();
759 pr_err("%s: unable to create sysfs entry\n", __func__);
765 late_initcall(bL_switcher_init);