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(kt: delta, div: ticks * resolution); |
49 | |
50 | snd_timer_interrupt(timer: stime->timer, ticks_left: ticks); |
51 | |
52 | guard(spinlock)(l: &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 | return ret; |
60 | } |
61 | |
62 | static int snd_hrtimer_open(struct snd_timer *t) |
63 | { |
64 | struct snd_hrtimer *stime; |
65 | |
66 | stime = kzalloc(size: sizeof(*stime), GFP_KERNEL); |
67 | if (!stime) |
68 | return -ENOMEM; |
69 | hrtimer_init(timer: &stime->hrt, CLOCK_MONOTONIC, mode: 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(timer: &stime->hrt); |
87 | kfree(objp: 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(timer: &stime->hrt, tim: ns_to_ktime(ns: t->sticks * resolution), |
100 | mode: 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(timer: &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(id: "hrtimer" , SNDRV_TIMER_GLOBAL_HRTIMER, |
137 | rtimer: &timer); |
138 | if (err < 0) |
139 | return err; |
140 | |
141 | timer->module = THIS_MODULE; |
142 | strcpy(p: timer->name, q: "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(timer: mytimer); |
162 | mytimer = NULL; |
163 | } |
164 | } |
165 | |
166 | module_init(snd_hrtimer_init); |
167 | module_exit(snd_hrtimer_exit); |
168 | |