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(&t->lock); 39 if (!t->running) 40 goto out; /* fast path */ 41 stime->in_callback = true; 42 ticks = t->sticks; 43 spin_unlock(&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(delta, ticks * resolution); 49 50 snd_timer_interrupt(stime->timer, ticks); 51 52 spin_lock(&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 out: 60 spin_unlock(&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(sizeof(*stime), GFP_KERNEL); 69 if (!stime) 70 return -ENOMEM; 71 hrtimer_init(&stime->hrt, CLOCK_MONOTONIC, 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(&t->lock); 84 t->running = 0; /* just to be sure */ 85 stime->in_callback = 1; /* skip start/stop */ 86 spin_unlock_irq(&t->lock); 87 88 hrtimer_cancel(&stime->hrt); 89 kfree(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(&stime->hrt, ns_to_ktime(t->sticks * resolution), 102 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(&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_TASKLET, 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("hrtimer", SNDRV_TIMER_GLOBAL_HRTIMER, 139 &timer); 140 if (err < 0) 141 return err; 142 143 timer->module = THIS_MODULE; 144 strcpy(timer->name, "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(mytimer); 164 mytimer = NULL; 165 } 166 } 167 168 module_init(snd_hrtimer_init); 169 module_exit(snd_hrtimer_exit); 170