LXR linux/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
  15MODULE_AUTHOR("Takashi Iwai <tiwai@suse.de>");
  16MODULE_DESCRIPTION("ALSA hrtimer backend");
  17MODULE_LICENSE("GPL");
  18
  19MODULE_ALIAS("snd-timer-" __stringify(SNDRV_TIMER_GLOBAL_HRTIMER));
  20
  21#define NANO_SEC        1000000000UL    /* 10^9 in sec */
  22static unsigned int resolution;
  23
  24struct snd_hrtimer {
  25        struct snd_timer *timer;
  26        struct hrtimer hrt;
  27        bool in_callback;
  28};
  29
  30static 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
  64static 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
  78static 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
  95static 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
 106static 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
 116static 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
 128static struct snd_timer *mytimer;
 129
 130static 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
 160static void __exit snd_hrtimer_exit(void)
 161{
 162        if (mytimer) {
 163                snd_timer_global_free(mytimer);
 164                mytimer = NULL;
 165        }
 166}
 167
 168module_init(snd_hrtimer_init);
 169module_exit(snd_hrtimer_exit);
 170