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1/*
2 * linux/kernel/time/tick-broadcast-hrtimer.c
3 * This file emulates a local clock event device
4 * via a pseudo clock device.
5 */
6#include <linux/cpu.h>
7#include <linux/err.h>
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>
16
17#include "tick-internal.h"
18
19static struct hrtimer bctimer;
20
21static int bc_shutdown(struct clock_event_device *evt)
22{
23 /*
24 * Note, we cannot cancel the timer here as we might
25 * run into the following live lock scenario:
26 *
27 * cpu 0 cpu1
28 * lock(broadcast_lock);
29 * hrtimer_interrupt()
30 * bc_handler()
31 * tick_handle_oneshot_broadcast();
32 * lock(broadcast_lock);
33 * hrtimer_cancel()
34 * wait_for_callback()
35 */
36 hrtimer_try_to_cancel(&bctimer);
37 return 0;
38}
39
40/*
41 * This is called from the guts of the broadcast code when the cpu
42 * which is about to enter idle has the earliest broadcast timer event.
43 */
44static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
45{
46 int bc_moved;
47 /*
48 * We try to cancel the timer first. If the callback is on
49 * flight on some other cpu then we let it handle it. If we
50 * were able to cancel the timer nothing can rearm it as we
51 * own broadcast_lock.
52 *
53 * However we can also be called from the event handler of
54 * ce_broadcast_hrtimer itself when it expires. We cannot
55 * restart the timer because we are in the callback, but we
56 * can set the expiry time and let the callback return
57 * HRTIMER_RESTART.
58 *
59 * Since we are in the idle loop at this point and because
60 * hrtimer_{start/cancel} functions call into tracing,
61 * calls to these functions must be bound within RCU_NONIDLE.
62 */
63 RCU_NONIDLE({
64 bc_moved = hrtimer_try_to_cancel(&bctimer) >= 0;
65 if (bc_moved)
66 hrtimer_start(&bctimer, expires,
67 HRTIMER_MODE_ABS_PINNED);});
68 if (bc_moved) {
69 /* Bind the "device" to the cpu */
70 bc->bound_on = smp_processor_id();
71 } else if (bc->bound_on == smp_processor_id()) {
72 hrtimer_set_expires(&bctimer, expires);
73 }
74 return 0;
75}
76
77static struct clock_event_device ce_broadcast_hrtimer = {
78 .set_state_shutdown = bc_shutdown,
79 .set_next_ktime = bc_set_next,
80 .features = CLOCK_EVT_FEAT_ONESHOT |
81 CLOCK_EVT_FEAT_KTIME |
82 CLOCK_EVT_FEAT_HRTIMER,
83 .rating = 0,
84 .bound_on = -1,
85 .min_delta_ns = 1,
86 .max_delta_ns = KTIME_MAX,
87 .min_delta_ticks = 1,
88 .max_delta_ticks = ULONG_MAX,
89 .mult = 1,
90 .shift = 0,
91 .cpumask = cpu_all_mask,
92};
93
94static enum hrtimer_restart bc_handler(struct hrtimer *t)
95{
96 ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
97
98 if (clockevent_state_oneshot(&ce_broadcast_hrtimer))
99 if (ce_broadcast_hrtimer.next_event.tv64 != KTIME_MAX)
100 return HRTIMER_RESTART;
101
102 return HRTIMER_NORESTART;
103}
104
105void tick_setup_hrtimer_broadcast(void)
106{
107 hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
108 bctimer.function = bc_handler;
109 clockevents_register_device(&ce_broadcast_hrtimer);
110}
1// SPDX-License-Identifier: GPL-2.0
2/*
3 * linux/kernel/time/tick-broadcast-hrtimer.c
4 * This file emulates a local clock event device
5 * via a pseudo clock device.
6 */
7#include <linux/cpu.h>
8#include <linux/err.h>
9#include <linux/hrtimer.h>
10#include <linux/interrupt.h>
11#include <linux/percpu.h>
12#include <linux/profile.h>
13#include <linux/clockchips.h>
14#include <linux/sched.h>
15#include <linux/smp.h>
16#include <linux/module.h>
17
18#include "tick-internal.h"
19
20static struct hrtimer bctimer;
21
22static int bc_shutdown(struct clock_event_device *evt)
23{
24 /*
25 * Note, we cannot cancel the timer here as we might
26 * run into the following live lock scenario:
27 *
28 * cpu 0 cpu1
29 * lock(broadcast_lock);
30 * hrtimer_interrupt()
31 * bc_handler()
32 * tick_handle_oneshot_broadcast();
33 * lock(broadcast_lock);
34 * hrtimer_cancel()
35 * wait_for_callback()
36 */
37 hrtimer_try_to_cancel(&bctimer);
38 return 0;
39}
40
41/*
42 * This is called from the guts of the broadcast code when the cpu
43 * which is about to enter idle has the earliest broadcast timer event.
44 */
45static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
46{
47 int bc_moved;
48 /*
49 * We try to cancel the timer first. If the callback is on
50 * flight on some other cpu then we let it handle it. If we
51 * were able to cancel the timer nothing can rearm it as we
52 * own broadcast_lock.
53 *
54 * However we can also be called from the event handler of
55 * ce_broadcast_hrtimer itself when it expires. We cannot
56 * restart the timer because we are in the callback, but we
57 * can set the expiry time and let the callback return
58 * HRTIMER_RESTART.
59 *
60 * Since we are in the idle loop at this point and because
61 * hrtimer_{start/cancel} functions call into tracing,
62 * calls to these functions must be bound within RCU_NONIDLE.
63 */
64 RCU_NONIDLE({
65 bc_moved = hrtimer_try_to_cancel(&bctimer) >= 0;
66 if (bc_moved)
67 hrtimer_start(&bctimer, expires,
68 HRTIMER_MODE_ABS_PINNED);});
69 if (bc_moved) {
70 /* Bind the "device" to the cpu */
71 bc->bound_on = smp_processor_id();
72 } else if (bc->bound_on == smp_processor_id()) {
73 hrtimer_set_expires(&bctimer, expires);
74 }
75 return 0;
76}
77
78static struct clock_event_device ce_broadcast_hrtimer = {
79 .name = "bc_hrtimer",
80 .set_state_shutdown = bc_shutdown,
81 .set_next_ktime = bc_set_next,
82 .features = CLOCK_EVT_FEAT_ONESHOT |
83 CLOCK_EVT_FEAT_KTIME |
84 CLOCK_EVT_FEAT_HRTIMER,
85 .rating = 0,
86 .bound_on = -1,
87 .min_delta_ns = 1,
88 .max_delta_ns = KTIME_MAX,
89 .min_delta_ticks = 1,
90 .max_delta_ticks = ULONG_MAX,
91 .mult = 1,
92 .shift = 0,
93 .cpumask = cpu_all_mask,
94};
95
96static enum hrtimer_restart bc_handler(struct hrtimer *t)
97{
98 ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
99
100 if (clockevent_state_oneshot(&ce_broadcast_hrtimer))
101 if (ce_broadcast_hrtimer.next_event != KTIME_MAX)
102 return HRTIMER_RESTART;
103
104 return HRTIMER_NORESTART;
105}
106
107void tick_setup_hrtimer_broadcast(void)
108{
109 hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
110 bctimer.function = bc_handler;
111 clockevents_register_device(&ce_broadcast_hrtimer);
112}