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