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         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);