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
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 scoped_guard(spinlock, &t->lock) {
39 if (!t->running)
40 return HRTIMER_NORESTART; /* fast path */
41 stime->in_callback = true;
42 ticks = t->sticks;
43 }
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 guard(spinlock)(&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 return ret;
60 }
61
62 static int snd_hrtimer_open(struct snd_timer *t)
63 {
64 struct snd_hrtimer *stime;
65
66 stime = kzalloc(sizeof(*stime), GFP_KERNEL);
67 if (!stime)
68 return -ENOMEM;
69 hrtimer_init(&stime->hrt, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
70 stime->timer = t;
71 stime->hrt.function = snd_hrtimer_callback;
72 t->private_data = stime;
73 return 0;
74 }
75
76 static 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
93 static 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
104 static 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
114 static 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
126 static struct snd_timer *mytimer;
127
128 static 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 strcpy(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
158 static void __exit snd_hrtimer_exit(void)
159 {
160 if (mytimer) {
161 snd_timer_global_free(mytimer);
162 mytimer = NULL;
163 }
164 }
165
166 module_init(snd_hrtimer_init);
167 module_exit(snd_hrtimer_exit);
168
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.