2 * linux/kernel/time/tick-broadcast-hrtimer.c
3 * This file emulates a local clock event device
4 * via a pseudo clock device.
8 #include <linux/hrtimer.h>
9 #include <linux/interrupt.h>
10 #include <linux/percpu.h>
11 #include <linux/profile.h>
12 #include <linux/clockchips.h>
13 #include <linux/sched.h>
14 #include <linux/smp.h>
15 #include <linux/module.h>
17 #include "tick-internal.h"
19 static struct hrtimer bctimer;
21 static void bc_set_mode(enum clock_event_mode mode,
22 struct clock_event_device *bc)
25 case CLOCK_EVT_MODE_UNUSED:
26 case CLOCK_EVT_MODE_SHUTDOWN:
28 * Note, we cannot cancel the timer here as we might
29 * run into the following live lock scenario:
32 * lock(broadcast_lock);
35 * tick_handle_oneshot_broadcast();
36 * lock(broadcast_lock);
40 hrtimer_try_to_cancel(&bctimer);
48 * This is called from the guts of the broadcast code when the cpu
49 * which is about to enter idle has the earliest broadcast timer event.
51 static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
55 * We try to cancel the timer first. If the callback is on
56 * flight on some other cpu then we let it handle it. If we
57 * were able to cancel the timer nothing can rearm it as we
60 * However we can also be called from the event handler of
61 * ce_broadcast_hrtimer itself when it expires. We cannot
62 * restart the timer because we are in the callback, but we
63 * can set the expiry time and let the callback return
66 * Since we are in the idle loop at this point and because
67 * hrtimer_{start/cancel} functions call into tracing,
68 * calls to these functions must be bound within RCU_NONIDLE.
71 bc_moved = hrtimer_try_to_cancel(&bctimer) >= 0;
73 hrtimer_start(&bctimer, expires,
74 HRTIMER_MODE_ABS_PINNED);});
76 /* Bind the "device" to the cpu */
77 bc->bound_on = smp_processor_id();
78 } else if (bc->bound_on == smp_processor_id()) {
79 hrtimer_set_expires(&bctimer, expires);
84 static struct clock_event_device ce_broadcast_hrtimer = {
85 .set_mode = bc_set_mode,
86 .set_next_ktime = bc_set_next,
87 .features = CLOCK_EVT_FEAT_ONESHOT |
88 CLOCK_EVT_FEAT_KTIME |
89 CLOCK_EVT_FEAT_HRTIMER,
93 .max_delta_ns = KTIME_MAX,
95 .max_delta_ticks = ULONG_MAX,
98 .cpumask = cpu_all_mask,
101 static enum hrtimer_restart bc_handler(struct hrtimer *t)
103 ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
105 switch (ce_broadcast_hrtimer.mode) {
106 case CLOCK_EVT_MODE_ONESHOT:
107 if (ce_broadcast_hrtimer.next_event.tv64 != KTIME_MAX)
108 return HRTIMER_RESTART;
110 return HRTIMER_NORESTART;
114 void tick_setup_hrtimer_broadcast(void)
116 hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
117 bctimer.function = bc_handler;
118 clockevents_register_device(&ce_broadcast_hrtimer);