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 16 MODULE_AUTHOR("Takashi Iwai <tiwai@suse.de>"); 17 MODULE_DESCRIPTION("ALSA hrtimer backend"); 18 MODULE_LICENSE("GPL"); 19 20 MODULE_ALIAS("snd-timer-" __stringify(SNDRV_TIMER_GLOBAL_HRTIMER)); 21 22 #define NANO_SEC 1000000000UL /* 10^9 in sec */ 23 static unsigned int resolution; 24 25 struct snd_hrtimer { 26 struct snd_timer *timer; 27 struct hrtimer hrt; 28 bool in_callback; 29 }; 30 31 static 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(hrt->base->get_time(), 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 63 static int snd_hrtimer_open(struct snd_timer *t) 64 { 65 struct snd_hrtimer *stime; 66 67 stime = kzalloc(sizeof(*stime), GFP_KERNEL); 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 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 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 } 157 158 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