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 void bc_set_mode(enum clock_event_mode mode,
22			struct clock_event_device *bc)
23{
24	switch (mode) {
25	case CLOCK_EVT_MODE_SHUTDOWN:
26		/*
27		 * Note, we cannot cancel the timer here as we might
28		 * run into the following live lock scenario:
29		 *
30		 * cpu 0		cpu1
31		 * lock(broadcast_lock);
32		 *			hrtimer_interrupt()
33		 *			bc_handler()
34		 *			   tick_handle_oneshot_broadcast();
35		 *			    lock(broadcast_lock);
36		 * hrtimer_cancel()
37		 *  wait_for_callback()
38		 */
39		hrtimer_try_to_cancel(&bctimer);
40		break;
41	default:
42		break;
43	}
44}
45
46/*
47 * This is called from the guts of the broadcast code when the cpu
48 * which is about to enter idle has the earliest broadcast timer event.
49 */
50static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
51{
52	int bc_moved;
53	/*
54	 * We try to cancel the timer first. If the callback is on
55	 * flight on some other cpu then we let it handle it. If we
56	 * were able to cancel the timer nothing can rearm it as we
57	 * own broadcast_lock.
58	 *
59	 * However we can also be called from the event handler of
60	 * ce_broadcast_hrtimer itself when it expires. We cannot
61	 * restart the timer because we are in the callback, but we
62	 * can set the expiry time and let the callback return
63	 * HRTIMER_RESTART.
64	 *
65	 * Since we are in the idle loop at this point and because
66	 * hrtimer_{start/cancel} functions call into tracing,
67	 * calls to these functions must be bound within RCU_NONIDLE.
68	 */
69	RCU_NONIDLE(bc_moved = (hrtimer_try_to_cancel(&bctimer) >= 0) ?
70		!hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED) :
71			0);
72	if (bc_moved) {
73		/* Bind the "device" to the cpu */
74		bc->bound_on = smp_processor_id();
75	} else if (bc->bound_on == smp_processor_id()) {
76		hrtimer_set_expires(&bctimer, expires);
77	}
78	return 0;
79}
80
81static struct clock_event_device ce_broadcast_hrtimer = {
82	.set_mode		= bc_set_mode,
83	.set_next_ktime		= bc_set_next,
84	.features		= CLOCK_EVT_FEAT_ONESHOT |
85				  CLOCK_EVT_FEAT_KTIME |
86				  CLOCK_EVT_FEAT_HRTIMER,
87	.rating			= 0,
88	.bound_on		= -1,
89	.min_delta_ns		= 1,
90	.max_delta_ns		= KTIME_MAX,
91	.min_delta_ticks	= 1,
92	.max_delta_ticks	= ULONG_MAX,
93	.mult			= 1,
94	.shift			= 0,
95	.cpumask		= cpu_all_mask,
96};
97
98static enum hrtimer_restart bc_handler(struct hrtimer *t)
99{
100	ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
101
102	if (ce_broadcast_hrtimer.next_event.tv64 == KTIME_MAX)
103		return HRTIMER_NORESTART;
104
105	return HRTIMER_RESTART;
106}
107
108void tick_setup_hrtimer_broadcast(void)
109{
110	hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
111	bctimer.function = bc_handler;
112	clockevents_register_device(&ce_broadcast_hrtimer);
113}
114