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 stime->timer = t; 70 hrtimer_setup(&stime->hrt, snd_hrtimer_callback, CLOCK_MONOTONIC, HRTIMER_MODE_REL); 71 t->private_data = stime; 72 return 0; 73 } 74 75 static int snd_hrtimer_close(struct snd_timer *t) 76 { 77 struct snd_hrtimer *stime = t->private_data; 78 79 if (stime) { 80 scoped_guard(spinlock_irq, &t->lock) { 81 t->running = 0; /* just to be sure */ 82 stime->in_callback = 1; /* skip start/stop */ 83 } 84 85 hrtimer_cancel(&stime->hrt); 86 kfree(stime); 87 t->private_data = NULL; 88 } 89 return 0; 90 } 91 92 static int snd_hrtimer_start(struct snd_timer *t) 93 { 94 struct snd_hrtimer *stime = t->private_data; 95 96 if (stime->in_callback) 97 return 0; 98 hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution), 99 HRTIMER_MODE_REL); 100 return 0; 101 } 102 103 static int snd_hrtimer_stop(struct snd_timer *t) 104 { 105 struct snd_hrtimer *stime = t->private_data; 106 107 if (stime->in_callback) 108 return 0; 109 hrtimer_try_to_cancel(&stime->hrt); 110 return 0; 111 } 112 113 static const struct snd_timer_hardware hrtimer_hw __initconst = { 114 .flags = SNDRV_TIMER_HW_AUTO | SNDRV_TIMER_HW_WORK, 115 .open = snd_hrtimer_open, 116 .close = snd_hrtimer_close, 117 .start = snd_hrtimer_start, 118 .stop = snd_hrtimer_stop, 119 }; 120 121 /* 122 * entry functions 123 */ 124 125 static struct snd_timer *mytimer; 126 127 static int __init snd_hrtimer_init(void) 128 { 129 struct snd_timer *timer; 130 int err; 131 132 resolution = hrtimer_resolution; 133 134 /* Create a new timer and set up the fields */ 135 err = snd_timer_global_new("hrtimer", SNDRV_TIMER_GLOBAL_HRTIMER, 136 &timer); 137 if (err < 0) 138 return err; 139 140 timer->module = THIS_MODULE; 141 strcpy(timer->name, "HR timer"); 142 timer->hw = hrtimer_hw; 143 timer->hw.resolution = resolution; 144 timer->hw.ticks = NANO_SEC / resolution; 145 timer->max_instances = 100; /* lower the limit */ 146 147 err = snd_timer_global_register(timer); 148 if (err < 0) { 149 snd_timer_global_free(timer); 150 return err; 151 } 152 mytimer = timer; /* remember this */ 153 154 return 0; 155 } 156 157 static void __exit snd_hrtimer_exit(void) 158 { 159 if (mytimer) { 160 snd_timer_global_free(mytimer); 161 mytimer = NULL; 162 } 163 } 164 165 module_init(snd_hrtimer_init); 166 module_exit(snd_hrtimer_exit); 167