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 | spin_lock(lock: &t->lock); |
39 | if (!t->running) |
40 | goto out; /* fast path */ |
41 | stime->in_callback = true; |
42 | ticks = t->sticks; |
43 | spin_unlock(lock: &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(kt: delta, div: ticks * resolution); |
49 | |
50 | snd_timer_interrupt(timer: stime->timer, ticks_left: ticks); |
51 | |
52 | spin_lock(lock: &t->lock); |
53 | if (t->running) { |
54 | hrtimer_add_expires_ns(timer: hrt, ns: t->sticks * resolution); |
55 | ret = HRTIMER_RESTART; |
56 | } |
57 | |
58 | stime->in_callback = false; |
59 | out: |
60 | spin_unlock(lock: &t->lock); |
61 | return ret; |
62 | } |
63 | |
64 | static int snd_hrtimer_open(struct snd_timer *t) |
65 | { |
66 | struct snd_hrtimer *stime; |
67 | |
68 | stime = kzalloc(size: sizeof(*stime), GFP_KERNEL); |
69 | if (!stime) |
70 | return -ENOMEM; |
71 | hrtimer_init(timer: &stime->hrt, CLOCK_MONOTONIC, mode: HRTIMER_MODE_REL); |
72 | stime->timer = t; |
73 | stime->hrt.function = snd_hrtimer_callback; |
74 | t->private_data = stime; |
75 | return 0; |
76 | } |
77 | |
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(lock: &t->lock); |
84 | t->running = 0; /* just to be sure */ |
85 | stime->in_callback = 1; /* skip start/stop */ |
86 | spin_unlock_irq(lock: &t->lock); |
87 | |
88 | hrtimer_cancel(timer: &stime->hrt); |
89 | kfree(objp: stime); |
90 | t->private_data = NULL; |
91 | } |
92 | return 0; |
93 | } |
94 | |
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(timer: &stime->hrt, tim: ns_to_ktime(ns: t->sticks * resolution), |
102 | mode: HRTIMER_MODE_REL); |
103 | return 0; |
104 | } |
105 | |
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(timer: &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 | |
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(id: "hrtimer" , SNDRV_TIMER_GLOBAL_HRTIMER, |
139 | rtimer: &timer); |
140 | if (err < 0) |
141 | return err; |
142 | |
143 | timer->module = THIS_MODULE; |
144 | strcpy(p: timer->name, q: "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 | |
160 | static void __exit snd_hrtimer_exit(void) |
161 | { |
162 | if (mytimer) { |
163 | snd_timer_global_free(timer: mytimer); |
164 | mytimer = NULL; |
165 | } |
166 | } |
167 | |
168 | module_init(snd_hrtimer_init); |
169 | module_exit(snd_hrtimer_exit); |
170 | |