1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Emulate a local clock event device via a pseudo clock device.
4 */
5#include <linux/cpu.h>
6#include <linux/err.h>
7#include <linux/hrtimer.h>
8#include <linux/interrupt.h>
9#include <linux/percpu.h>
10#include <linux/profile.h>
11#include <linux/clockchips.h>
12#include <linux/sched.h>
13#include <linux/smp.h>
14#include <linux/module.h>
15
16#include "tick-internal.h"
17
18static struct hrtimer bctimer;
19
20static int bc_shutdown(struct clock_event_device *evt)
21{
22	/*
23	 * Note, we cannot cancel the timer here as we might
24	 * run into the following live lock scenario:
25	 *
26	 * cpu 0		cpu1
27	 * lock(broadcast_lock);
28	 *			hrtimer_interrupt()
29	 *			bc_handler()
30	 *			   tick_handle_oneshot_broadcast();
31	 *			    lock(broadcast_lock);
32	 * hrtimer_cancel()
33	 *  wait_for_callback()
34	 */
35	hrtimer_try_to_cancel(&bctimer);
36	return 0;
37}
38
39/*
40 * This is called from the guts of the broadcast code when the cpu
41 * which is about to enter idle has the earliest broadcast timer event.
42 */
43static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
44{
45	/*
46	 * This is called either from enter/exit idle code or from the
47	 * broadcast handler. In all cases tick_broadcast_lock is held.
48	 *
49	 * hrtimer_cancel() cannot be called here neither from the
50	 * broadcast handler nor from the enter/exit idle code. The idle
51	 * code can run into the problem described in bc_shutdown() and the
52	 * broadcast handler cannot wait for itself to complete for obvious
53	 * reasons.
54	 *
55	 * Each caller tries to arm the hrtimer on its own CPU, but if the
56	 * hrtimer callback function is currently running, then
57	 * hrtimer_start() cannot move it and the timer stays on the CPU on
58	 * which it is assigned at the moment.
59	 */
60	hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED_HARD);
61	/*
62	 * The core tick broadcast mode expects bc->bound_on to be set
63	 * correctly to prevent a CPU which has the broadcast hrtimer
64	 * armed from going deep idle.
65	 *
66	 * As tick_broadcast_lock is held, nothing can change the cpu
67	 * base which was just established in hrtimer_start() above. So
68	 * the below access is safe even without holding the hrtimer
69	 * base lock.
70	 */
71	bc->bound_on = bctimer.base->cpu_base->cpu;
72
73	return 0;
74}
75
76static struct clock_event_device ce_broadcast_hrtimer = {
77	.name			= "bc_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_possible_mask,
92};
93
94static enum hrtimer_restart bc_handler(struct hrtimer *t)
95{
96	ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
97
98	return HRTIMER_NORESTART;
99}
100
101void tick_setup_hrtimer_broadcast(void)
102{
103	hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
104	bctimer.function = bc_handler;
105	clockevents_register_device(&ce_broadcast_hrtimer);
106}
107