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/module.h>
10 #include <linux/moduleparam.h>
11 #include <linux/hrtimer.h>
12 #include <sound/core.h>
13 #include <sound/timer.h>
14
15 MODULE_AUTHOR("Takashi Iwai <tiwai@suse.de>");
16 MODULE_DESCRIPTION("ALSA hrtimer backend");
17 MODULE_LICENSE("GPL");
18
19 MODULE_ALIAS("snd-timer-" __stringify(SNDRV_TIMER_GLOBAL_HRTIMER));
20
21 #define NANO_SEC 1000000000UL /* 10^9 in sec */
22 static unsigned int resolution;
23
24 struct snd_hrtimer {
25 struct snd_timer *timer;
26 struct hrtimer hrt;
27 bool in_callback;
28 };
29
snd_hrtimer_callback(struct hrtimer * hrt)30 static enum hrtimer_restart snd_hrtimer_callback(struct hrtimer *hrt)
31 {
32 struct snd_hrtimer *stime = container_of(hrt, struct snd_hrtimer, hrt);
33 struct snd_timer *t = stime->timer;
34 ktime_t delta;
35 unsigned long ticks;
36 enum hrtimer_restart ret = HRTIMER_NORESTART;
37
38 spin_lock(&t->lock);
39 if (!t->running)
40 goto out; /* fast path */
41 stime->in_callback = true;
42 ticks = t->sticks;
43 spin_unlock(&t->lock);
44
45 /* calculate the drift */
46 delta = ktime_sub(hrt->base->get_time(), hrtimer_get_expires(hrt));
47 if (delta > 0)
48 ticks += ktime_divns(delta, ticks * resolution);
49
50 snd_timer_interrupt(stime->timer, ticks);
51
52 spin_lock(&t->lock);
53 if (t->running) {
54 hrtimer_add_expires_ns(hrt, t->sticks * resolution);
55 ret = HRTIMER_RESTART;
56 }
57
58 stime->in_callback = false;
59 out:
60 spin_unlock(&t->lock);
61 return ret;
62 }
63
snd_hrtimer_open(struct snd_timer * t)64 static int snd_hrtimer_open(struct snd_timer *t)
65 {
66 struct snd_hrtimer *stime;
67
68 stime = kzalloc(sizeof(*stime), GFP_KERNEL);
69 if (!stime)
70 return -ENOMEM;
71 hrtimer_init(&stime->hrt, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
72 stime->timer = t;
73 stime->hrt.function = snd_hrtimer_callback;
74 t->private_data = stime;
75 return 0;
76 }
77
snd_hrtimer_close(struct snd_timer * t)78 static int snd_hrtimer_close(struct snd_timer *t)
79 {
80 struct snd_hrtimer *stime = t->private_data;
81
82 if (stime) {
83 spin_lock_irq(&t->lock);
84 t->running = 0; /* just to be sure */
85 stime->in_callback = 1; /* skip start/stop */
86 spin_unlock_irq(&t->lock);
87
88 hrtimer_cancel(&stime->hrt);
89 kfree(stime);
90 t->private_data = NULL;
91 }
92 return 0;
93 }
94
snd_hrtimer_start(struct snd_timer * t)95 static int snd_hrtimer_start(struct snd_timer *t)
96 {
97 struct snd_hrtimer *stime = t->private_data;
98
99 if (stime->in_callback)
100 return 0;
101 hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution),
102 HRTIMER_MODE_REL);
103 return 0;
104 }
105
snd_hrtimer_stop(struct snd_timer * t)106 static int snd_hrtimer_stop(struct snd_timer *t)
107 {
108 struct snd_hrtimer *stime = t->private_data;
109
110 if (stime->in_callback)
111 return 0;
112 hrtimer_try_to_cancel(&stime->hrt);
113 return 0;
114 }
115
116 static const struct snd_timer_hardware hrtimer_hw __initconst = {
117 .flags = SNDRV_TIMER_HW_AUTO | SNDRV_TIMER_HW_WORK,
118 .open = snd_hrtimer_open,
119 .close = snd_hrtimer_close,
120 .start = snd_hrtimer_start,
121 .stop = snd_hrtimer_stop,
122 };
123
124 /*
125 * entry functions
126 */
127
128 static struct snd_timer *mytimer;
129
snd_hrtimer_init(void)130 static int __init snd_hrtimer_init(void)
131 {
132 struct snd_timer *timer;
133 int err;
134
135 resolution = hrtimer_resolution;
136
137 /* Create a new timer and set up the fields */
138 err = snd_timer_global_new("hrtimer", SNDRV_TIMER_GLOBAL_HRTIMER,
139 &timer);
140 if (err < 0)
141 return err;
142
143 timer->module = THIS_MODULE;
144 strcpy(timer->name, "HR timer");
145 timer->hw = hrtimer_hw;
146 timer->hw.resolution = resolution;
147 timer->hw.ticks = NANO_SEC / resolution;
148 timer->max_instances = 100; /* lower the limit */
149
150 err = snd_timer_global_register(timer);
151 if (err < 0) {
152 snd_timer_global_free(timer);
153 return err;
154 }
155 mytimer = timer; /* remember this */
156
157 return 0;
158 }
159
snd_hrtimer_exit(void)160 static void __exit snd_hrtimer_exit(void)
161 {
162 if (mytimer) {
163 snd_timer_global_free(mytimer);
164 mytimer = NULL;
165 }
166 }
167
168 module_init(snd_hrtimer_init);
169 module_exit(snd_hrtimer_exit);
170