hrtimer.c

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/*
 * 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/slab.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 <[email protected]>");
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;
    atomic_t running;
};

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;
    unsigned long oruns;

    if (!atomic_read(&stime->running))
        return HRTIMER_NORESTART;

    oruns = hrtimer_forward_now(hrt, ns_to_ktime(t->sticks * resolution));
    snd_timer_interrupt(stime->timer, t->sticks * oruns);

    if (!atomic_read(&stime->running))
        return HRTIMER_NORESTART;
    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;
    atomic_set(&stime->running, 0);
    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;

    atomic_set(&stime->running, 0);
    hrtimer_cancel(&stime->hrt);
    hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution),
              HRTIMER_MODE_REL);
    atomic_set(&stime->running, 1);
    return 0;
}

static int snd_hrtimer_stop(struct snd_timer *t)
{
    struct snd_hrtimer *stime = t->private_data;
    atomic_set(&stime->running, 0);
    return 0;
}

static struct snd_timer_hardware hrtimer_hw = {
    .flags =    SNDRV_TIMER_HW_AUTO | SNDRV_TIMER_HW_TASKLET,
    .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);