LXR linux/sound/core/hrtimer.c

   1/*
   2 * ALSA timer back-end using hrtimer
   3 * Copyright (C) 2008 Takashi Iwai
   4 *
   5 *   This program is free software; you can redistribute it and/or modify
   6 *   it under the terms of the GNU General Public License as published by
   7 *   the Free Software Foundation; either version 2 of the License, or
   8 *   (at your option) any later version.
   9 *
  10 *   This program is distributed in the hope that it will be useful,
  11 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 *   GNU General Public License for more details.
  14 *
  15 *   You should have received a copy of the GNU General Public License
  16 *   along with this program; if not, write to the Free Software
  17 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
  18 *
  19 */
  20
  21#include <linux/init.h>
  22#include <linux/slab.h>
  23#include <linux/module.h>
  24#include <linux/moduleparam.h>
  25#include <linux/hrtimer.h>
  26#include <sound/core.h>
  27#include <sound/timer.h>
  28
  29MODULE_AUTHOR("Takashi Iwai <tiwai@suse.de>");
  30MODULE_DESCRIPTION("ALSA hrtimer backend");
  31MODULE_LICENSE("GPL");
  32
  33MODULE_ALIAS("snd-timer-" __stringify(SNDRV_TIMER_GLOBAL_HRTIMER));
  34
  35#define NANO_SEC        1000000000UL    /* 10^9 in sec */
  36static unsigned int resolution;
  37
  38struct snd_hrtimer {
  39        struct snd_timer *timer;
  40        struct hrtimer hrt;
  41        bool in_callback;
  42};
  43
  44static enum hrtimer_restart snd_hrtimer_callback(struct hrtimer *hrt)
  45{
  46        struct snd_hrtimer *stime = container_of(hrt, struct snd_hrtimer, hrt);
  47        struct snd_timer *t = stime->timer;
  48        ktime_t delta;
  49        unsigned long ticks;
  50        enum hrtimer_restart ret = HRTIMER_NORESTART;
  51
  52        spin_lock(&t->lock);
  53        if (!t->running)
  54                goto out; /* fast path */
  55        stime->in_callback = true;
  56        ticks = t->sticks;
  57        spin_unlock(&t->lock);
  58
  59        /* calculate the drift */
  60        delta = ktime_sub(hrt->base->get_time(), hrtimer_get_expires(hrt));
  61        if (delta > 0)
  62                ticks += ktime_divns(delta, ticks * resolution);
  63
  64        snd_timer_interrupt(stime->timer, ticks);
  65
  66        spin_lock(&t->lock);
  67        if (t->running) {
  68                hrtimer_add_expires_ns(hrt, t->sticks * resolution);
  69                ret = HRTIMER_RESTART;
  70        }
  71
  72        stime->in_callback = false;
  73 out:
  74        spin_unlock(&t->lock);
  75        return ret;
  76}
  77
  78static int snd_hrtimer_open(struct snd_timer *t)
  79{
  80        struct snd_hrtimer *stime;
  81
  82        stime = kzalloc(sizeof(*stime), GFP_KERNEL);
  83        if (!stime)
  84                return -ENOMEM;
  85        hrtimer_init(&stime->hrt, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
  86        stime->timer = t;
  87        stime->hrt.function = snd_hrtimer_callback;
  88        t->private_data = stime;
  89        return 0;
  90}
  91
  92static int snd_hrtimer_close(struct snd_timer *t)
  93{
  94        struct snd_hrtimer *stime = t->private_data;
  95
  96        if (stime) {
  97                spin_lock_irq(&t->lock);
  98                t->running = 0; /* just to be sure */
  99                stime->in_callback = 1; /* skip start/stop */
 100                spin_unlock_irq(&t->lock);
 101
 102                hrtimer_cancel(&stime->hrt);
 103                kfree(stime);
 104                t->private_data = NULL;
 105        }
 106        return 0;
 107}
 108
 109static int snd_hrtimer_start(struct snd_timer *t)
 110{
 111        struct snd_hrtimer *stime = t->private_data;
 112
 113        if (stime->in_callback)
 114                return 0;
 115        hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution),
 116                      HRTIMER_MODE_REL);
 117        return 0;
 118}
 119
 120static int snd_hrtimer_stop(struct snd_timer *t)
 121{
 122        struct snd_hrtimer *stime = t->private_data;
 123
 124        if (stime->in_callback)
 125                return 0;
 126        hrtimer_try_to_cancel(&stime->hrt);
 127        return 0;
 128}
 129
 130static const struct snd_timer_hardware hrtimer_hw __initconst = {
 131        .flags =        SNDRV_TIMER_HW_AUTO | SNDRV_TIMER_HW_TASKLET,
 132        .open =         snd_hrtimer_open,
 133        .close =        snd_hrtimer_close,
 134        .start =        snd_hrtimer_start,
 135        .stop =         snd_hrtimer_stop,
 136};
 137
 138/*
 139 * entry functions
 140 */
 141
 142static struct snd_timer *mytimer;
 143
 144static int __init snd_hrtimer_init(void)
 145{
 146        struct snd_timer *timer;
 147        int err;
 148
 149        resolution = hrtimer_resolution;
 150
 151        /* Create a new timer and set up the fields */
 152        err = snd_timer_global_new("hrtimer", SNDRV_TIMER_GLOBAL_HRTIMER,
 153                                   &timer);
 154        if (err < 0)
 155                return err;
 156
 157        timer->module = THIS_MODULE;
 158        strcpy(timer->name, "HR timer");
 159        timer->hw = hrtimer_hw;
 160        timer->hw.resolution = resolution;
 161        timer->hw.ticks = NANO_SEC / resolution;
 162        timer->max_instances = 100; /* lower the limit */
 163
 164        err = snd_timer_global_register(timer);
 165        if (err < 0) {
 166                snd_timer_global_free(timer);
 167                return err;
 168        }
 169        mytimer = timer; /* remember this */
 170
 171        return 0;
 172}
 173
 174static void __exit snd_hrtimer_exit(void)
 175{
 176        if (mytimer) {
 177                snd_timer_global_free(mytimer);
 178                mytimer = NULL;
 179        }
 180}
 181
 182module_init(snd_hrtimer_init);
 183module_exit(snd_hrtimer_exit);
 184