1/*
2 * Generic entry point for the idle threads
3 */
4#include <linux/sched.h>
5#include <linux/cpu.h>
6#include <linux/cpuidle.h>
7#include <linux/tick.h>
8#include <linux/mm.h>
9#include <linux/stackprotector.h>
10#include <linux/suspend.h>
11
12#include <asm/tlb.h>
13
14#include <trace/events/power.h>
15
16#include "sched.h"
17
18static int __read_mostly cpu_idle_force_poll;
19
20void cpu_idle_poll_ctrl(bool enable)
21{
22	if (enable) {
23		cpu_idle_force_poll++;
24	} else {
25		cpu_idle_force_poll--;
26		WARN_ON_ONCE(cpu_idle_force_poll < 0);
27	}
28}
29
30#ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
31static int __init cpu_idle_poll_setup(char *__unused)
32{
33	cpu_idle_force_poll = 1;
34	return 1;
35}
36__setup("nohlt", cpu_idle_poll_setup);
37
38static int __init cpu_idle_nopoll_setup(char *__unused)
39{
40	cpu_idle_force_poll = 0;
41	return 1;
42}
43__setup("hlt", cpu_idle_nopoll_setup);
44#endif
45
46static inline int cpu_idle_poll(void)
47{
48	rcu_idle_enter();
49	trace_cpu_idle_rcuidle(0, smp_processor_id());
50	local_irq_enable();
51	while (!tif_need_resched() &&
52		(cpu_idle_force_poll || tick_check_broadcast_expired()))
53		cpu_relax();
54	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
55	rcu_idle_exit();
56	return 1;
57}
58
59/* Weak implementations for optional arch specific functions */
60void __weak arch_cpu_idle_prepare(void) { }
61void __weak arch_cpu_idle_enter(void) { }
62void __weak arch_cpu_idle_exit(void) { }
63void __weak arch_cpu_idle_dead(void) { }
64void __weak arch_cpu_idle(void)
65{
66	cpu_idle_force_poll = 1;
67	local_irq_enable();
68}
69
70/**
71 * cpuidle_idle_call - the main idle function
72 *
73 * NOTE: no locks or semaphores should be used here
74 *
75 * On archs that support TIF_POLLING_NRFLAG, is called with polling
76 * set, and it returns with polling set.  If it ever stops polling, it
77 * must clear the polling bit.
78 */
79static void cpuidle_idle_call(void)
80{
81	struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
82	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
83	int next_state, entered_state;
84	bool reflect;
85
86	/*
87	 * Check if the idle task must be rescheduled. If it is the
88	 * case, exit the function after re-enabling the local irq.
89	 */
90	if (need_resched()) {
91		local_irq_enable();
92		return;
93	}
94
95	/*
96	 * During the idle period, stop measuring the disabled irqs
97	 * critical sections latencies
98	 */
99	stop_critical_timings();
100
101	/*
102	 * Tell the RCU framework we are entering an idle section,
103	 * so no more rcu read side critical sections and one more
104	 * step to the grace period
105	 */
106	rcu_idle_enter();
107
108	if (cpuidle_not_available(drv, dev))
109		goto use_default;
110
111	/*
112	 * Suspend-to-idle ("freeze") is a system state in which all user space
113	 * has been frozen, all I/O devices have been suspended and the only
114	 * activity happens here and in iterrupts (if any).  In that case bypass
115	 * the cpuidle governor and go stratight for the deepest idle state
116	 * available.  Possibly also suspend the local tick and the entire
117	 * timekeeping to prevent timer interrupts from kicking us out of idle
118	 * until a proper wakeup interrupt happens.
119	 */
120	if (idle_should_freeze()) {
121		entered_state = cpuidle_enter_freeze(drv, dev);
122		if (entered_state >= 0) {
123			local_irq_enable();
124			goto exit_idle;
125		}
126
127		reflect = false;
128		next_state = cpuidle_find_deepest_state(drv, dev);
129	} else {
130		reflect = true;
131		/*
132		 * Ask the cpuidle framework to choose a convenient idle state.
133		 */
134		next_state = cpuidle_select(drv, dev);
135	}
136	/* Fall back to the default arch idle method on errors. */
137	if (next_state < 0)
138		goto use_default;
139
140	/*
141	 * The idle task must be scheduled, it is pointless to
142	 * go to idle, just update no idle residency and get
143	 * out of this function
144	 */
145	if (current_clr_polling_and_test()) {
146		dev->last_residency = 0;
147		entered_state = next_state;
148		local_irq_enable();
149		goto exit_idle;
150	}
151
152	/* Take note of the planned idle state. */
153	idle_set_state(this_rq(), &drv->states[next_state]);
154
155	/*
156	 * Enter the idle state previously returned by the governor decision.
157	 * This function will block until an interrupt occurs and will take
158	 * care of re-enabling the local interrupts
159	 */
160	entered_state = cpuidle_enter(drv, dev, next_state);
161
162	/* The cpu is no longer idle or about to enter idle. */
163	idle_set_state(this_rq(), NULL);
164
165	if (entered_state == -EBUSY)
166		goto use_default;
167
168	/*
169	 * Give the governor an opportunity to reflect on the outcome
170	 */
171	if (reflect)
172		cpuidle_reflect(dev, entered_state);
173
174exit_idle:
175	__current_set_polling();
176
177	/*
178	 * It is up to the idle functions to reenable local interrupts
179	 */
180	if (WARN_ON_ONCE(irqs_disabled()))
181		local_irq_enable();
182
183	rcu_idle_exit();
184	start_critical_timings();
185	return;
186
187use_default:
188	/*
189	 * We can't use the cpuidle framework, let's use the default
190	 * idle routine.
191	 */
192	if (current_clr_polling_and_test())
193		local_irq_enable();
194	else
195		arch_cpu_idle();
196
197	goto exit_idle;
198}
199
200DEFINE_PER_CPU(bool, cpu_dead_idle);
201
202/*
203 * Generic idle loop implementation
204 *
205 * Called with polling cleared.
206 */
207static void cpu_idle_loop(void)
208{
209	while (1) {
210		/*
211		 * If the arch has a polling bit, we maintain an invariant:
212		 *
213		 * Our polling bit is clear if we're not scheduled (i.e. if
214		 * rq->curr != rq->idle).  This means that, if rq->idle has
215		 * the polling bit set, then setting need_resched is
216		 * guaranteed to cause the cpu to reschedule.
217		 */
218
219		__current_set_polling();
220		tick_nohz_idle_enter();
221
222		while (!need_resched()) {
223			check_pgt_cache();
224			rmb();
225
226			if (cpu_is_offline(smp_processor_id())) {
227				rcu_cpu_notify(NULL, CPU_DYING_IDLE,
228					       (void *)(long)smp_processor_id());
229				smp_mb(); /* all activity before dead. */
230				this_cpu_write(cpu_dead_idle, true);
231				arch_cpu_idle_dead();
232			}
233
234			local_irq_disable();
235			arch_cpu_idle_enter();
236
237			/*
238			 * In poll mode we reenable interrupts and spin.
239			 *
240			 * Also if we detected in the wakeup from idle
241			 * path that the tick broadcast device expired
242			 * for us, we don't want to go deep idle as we
243			 * know that the IPI is going to arrive right
244			 * away
245			 */
246			if (cpu_idle_force_poll || tick_check_broadcast_expired())
247				cpu_idle_poll();
248			else
249				cpuidle_idle_call();
250
251			arch_cpu_idle_exit();
252		}
253
254		/*
255		 * Since we fell out of the loop above, we know
256		 * TIF_NEED_RESCHED must be set, propagate it into
257		 * PREEMPT_NEED_RESCHED.
258		 *
259		 * This is required because for polling idle loops we will
260		 * not have had an IPI to fold the state for us.
261		 */
262		preempt_set_need_resched();
263		tick_nohz_idle_exit();
264		__current_clr_polling();
265
266		/*
267		 * We promise to call sched_ttwu_pending and reschedule
268		 * if need_resched is set while polling is set.  That
269		 * means that clearing polling needs to be visible
270		 * before doing these things.
271		 */
272		smp_mb__after_atomic();
273
274		sched_ttwu_pending();
275		schedule_preempt_disabled();
276	}
277}
278
279void cpu_startup_entry(enum cpuhp_state state)
280{
281	/*
282	 * This #ifdef needs to die, but it's too late in the cycle to
283	 * make this generic (arm and sh have never invoked the canary
284	 * init for the non boot cpus!). Will be fixed in 3.11
285	 */
286#ifdef CONFIG_X86
287	/*
288	 * If we're the non-boot CPU, nothing set the stack canary up
289	 * for us. The boot CPU already has it initialized but no harm
290	 * in doing it again. This is a good place for updating it, as
291	 * we wont ever return from this function (so the invalid
292	 * canaries already on the stack wont ever trigger).
293	 */
294	boot_init_stack_canary();
295#endif
296	arch_cpu_idle_prepare();
297	cpu_idle_loop();
298}
299