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1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * ALSA timer back-end using hrtimer
4 * Copyright (C) 2008 Takashi Iwai
5 */
6
7#include <linux/init.h>
8#include <linux/slab.h>
9#include <linux/string.h>
10#include <linux/module.h>
11#include <linux/moduleparam.h>
12#include <linux/hrtimer.h>
13#include <sound/core.h>
14#include <sound/timer.h>
15
16MODULE_AUTHOR("Takashi Iwai <[email protected]>");
17MODULE_DESCRIPTION("ALSA hrtimer backend");
18MODULE_LICENSE("GPL");
19
20MODULE_ALIAS("snd-timer-" __stringify(SNDRV_TIMER_GLOBAL_HRTIMER));
21
22#define NANO_SEC 1000000000UL /* 10^9 in sec */
23static unsigned int resolution __ro_after_init;
24
25struct snd_hrtimer {
26 struct snd_timer *timer;
27 struct hrtimer hrt;
28 bool in_callback;
29};
30
31static enum hrtimer_restart snd_hrtimer_callback(struct hrtimer *hrt)
32{
33 struct snd_hrtimer *stime = container_of(hrt, struct snd_hrtimer, hrt);
34 struct snd_timer *t = stime->timer;
35 ktime_t delta;
36 unsigned long ticks;
37 enum hrtimer_restart ret = HRTIMER_NORESTART;
38
39 scoped_guard(spinlock, &t->lock) {
40 if (!t->running)
41 return HRTIMER_NORESTART; /* fast path */
42 stime->in_callback = true;
43 ticks = t->sticks;
44 }
45
46 /* calculate the drift */
47 delta = ktime_sub(hrtimer_cb_get_time(hrt), hrtimer_get_expires(hrt));
48 if (delta > 0)
49 ticks += ktime_divns(delta, ticks * resolution);
50
51 snd_timer_interrupt(stime->timer, ticks);
52
53 guard(spinlock)(&t->lock);
54 if (t->running) {
55 hrtimer_add_expires_ns(hrt, t->sticks * resolution);
56 ret = HRTIMER_RESTART;
57 }
58
59 stime->in_callback = false;
60 return ret;
61}
62
63static int snd_hrtimer_open(struct snd_timer *t)
64{
65 struct snd_hrtimer *stime;
66
67 stime = kzalloc_obj(*stime);
68 if (!stime)
69 return -ENOMEM;
70 stime->timer = t;
71 hrtimer_setup(&stime->hrt, snd_hrtimer_callback, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
72 t->private_data = stime;
73 return 0;
74}
75
76static int snd_hrtimer_close(struct snd_timer *t)
77{
78 struct snd_hrtimer *stime = t->private_data;
79
80 if (stime) {
81 scoped_guard(spinlock_irq, &t->lock) {
82 t->running = 0; /* just to be sure */
83 stime->in_callback = 1; /* skip start/stop */
84 }
85
86 hrtimer_cancel(&stime->hrt);
87 kfree(stime);
88 t->private_data = NULL;
89 }
90 return 0;
91}
92
93static int snd_hrtimer_start(struct snd_timer *t)
94{
95 struct snd_hrtimer *stime = t->private_data;
96
97 if (stime->in_callback)
98 return 0;
99 hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution),
100 HRTIMER_MODE_REL);
101 return 0;
102}
103
104static int snd_hrtimer_stop(struct snd_timer *t)
105{
106 struct snd_hrtimer *stime = t->private_data;
107
108 if (stime->in_callback)
109 return 0;
110 hrtimer_try_to_cancel(&stime->hrt);
111 return 0;
112}
113
114static const struct snd_timer_hardware hrtimer_hw __initconst = {
115 .flags = SNDRV_TIMER_HW_AUTO | SNDRV_TIMER_HW_WORK,
116 .open = snd_hrtimer_open,
117 .close = snd_hrtimer_close,
118 .start = snd_hrtimer_start,
119 .stop = snd_hrtimer_stop,
120};
121
122/*
123 * entry functions
124 */
125
126static struct snd_timer *mytimer;
127
128static int __init snd_hrtimer_init(void)
129{
130 struct snd_timer *timer;
131 int err;
132
133 resolution = hrtimer_resolution;
134
135 /* Create a new timer and set up the fields */
136 err = snd_timer_global_new("hrtimer", SNDRV_TIMER_GLOBAL_HRTIMER,
137 &timer);
138 if (err < 0)
139 return err;
140
141 timer->module = THIS_MODULE;
142 strscpy(timer->name, "HR timer");
143 timer->hw = hrtimer_hw;
144 timer->hw.resolution = resolution;
145 timer->hw.ticks = NANO_SEC / resolution;
146 timer->max_instances = 100; /* lower the limit */
147
148 err = snd_timer_global_register(timer);
149 if (err < 0) {
150 snd_timer_global_free(timer);
151 return err;
152 }
153 mytimer = timer; /* remember this */
154
155 return 0;
156}
157
158static void __exit snd_hrtimer_exit(void)
159{
160 if (mytimer) {
161 snd_timer_global_free(mytimer);
162 mytimer = NULL;
163 }
164}
165
166module_init(snd_hrtimer_init);
167module_exit(snd_hrtimer_exit);