sound/core/hrtimer.c

   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_WORK,
 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);