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hrtimer.c

/*
 * ALSA timer back-end using hrtimer
 * Copyright (C) 2008 Takashi Iwai
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
 *
 */

#include <linux/init.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/hrtimer.h>
#include <sound/core.h>
#include <sound/timer.h>

MODULE_AUTHOR("Takashi Iwai <tiwai@suse.de>");
MODULE_DESCRIPTION("ALSA hrtimer backend");
MODULE_LICENSE("GPL");

MODULE_ALIAS("snd-timer-" __stringify(SNDRV_TIMER_GLOBAL_HRTIMER));

#define NANO_SEC  1000000000UL      /* 10^9 in sec */
static unsigned int resolution;

struct snd_hrtimer {
      struct snd_timer *timer;
      struct hrtimer hrt;
};

static enum hrtimer_restart snd_hrtimer_callback(struct hrtimer *hrt)
{
      struct snd_hrtimer *stime = container_of(hrt, struct snd_hrtimer, hrt);
      struct snd_timer *t = stime->timer;
      hrtimer_forward_now(hrt, ns_to_ktime(t->sticks * resolution));
      snd_timer_interrupt(stime->timer, t->sticks);
      return HRTIMER_RESTART;
}

static int snd_hrtimer_open(struct snd_timer *t)
{
      struct snd_hrtimer *stime;

      stime = kmalloc(sizeof(*stime), GFP_KERNEL);
      if (!stime)
            return -ENOMEM;
      hrtimer_init(&stime->hrt, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
      stime->timer = t;
      stime->hrt.function = snd_hrtimer_callback;
      t->private_data = stime;
      return 0;
}

static int snd_hrtimer_close(struct snd_timer *t)
{
      struct snd_hrtimer *stime = t->private_data;

      if (stime) {
            hrtimer_cancel(&stime->hrt);
            kfree(stime);
            t->private_data = NULL;
      }
      return 0;
}

static int snd_hrtimer_start(struct snd_timer *t)
{
      struct snd_hrtimer *stime = t->private_data;

      hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution),
                  HRTIMER_MODE_REL);
      return 0;
}

static int snd_hrtimer_stop(struct snd_timer *t)
{
      struct snd_hrtimer *stime = t->private_data;

      hrtimer_cancel(&stime->hrt);
      return 0;
}

static struct snd_timer_hardware hrtimer_hw = {
      .flags =    SNDRV_TIMER_HW_AUTO,
      .open =           snd_hrtimer_open,
      .close =    snd_hrtimer_close,
      .start =    snd_hrtimer_start,
      .stop =           snd_hrtimer_stop,
};

/*
 * entry functions
 */

static struct snd_timer *mytimer;

static int __init snd_hrtimer_init(void)
{
      struct snd_timer *timer;
      struct timespec tp;
      int err;

      hrtimer_get_res(CLOCK_MONOTONIC, &tp);
      if (tp.tv_sec > 0 || !tp.tv_nsec) {
            snd_printk(KERN_ERR
                     "snd-hrtimer: Invalid resolution %u.%09u",
                     (unsigned)tp.tv_sec, (unsigned)tp.tv_nsec);
            return -EINVAL;
      }
      resolution = tp.tv_nsec;

      /* Create a new timer and set up the fields */
      err = snd_timer_global_new("hrtimer", SNDRV_TIMER_GLOBAL_HRTIMER,
                           &timer);
      if (err < 0)
            return err;

      timer->module = THIS_MODULE;
      strcpy(timer->name, "HR timer");
      timer->hw = hrtimer_hw;
      timer->hw.resolution = resolution;
      timer->hw.ticks = NANO_SEC / resolution;

      err = snd_timer_global_register(timer);
      if (err < 0) {
            snd_timer_global_free(timer);
            return err;
      }
      mytimer = timer; /* remember this */

      return 0;
}

static void __exit snd_hrtimer_exit(void)
{
      if (mytimer) {
            snd_timer_global_free(mytimer);
            mytimer = NULL;
      }
}

module_init(snd_hrtimer_init);
module_exit(snd_hrtimer_exit);

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