High-resolution timer driver

  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 
 29 MODULE_AUTHOR("Takashi Iwai <tiwai@suse.de>");
 30 MODULE_DESCRIPTION("ALSA hrtimer backend");
 31 MODULE_LICENSE("GPL");
 32 
 33 MODULE_ALIAS("snd-timer-" __stringify(SNDRV_TIMER_GLOBAL_HRTIMER));
 34 
 35 #define NANO_SEC        1000000000UL    /* 10^9 in sec */
 36 static unsigned int resolution;
 37 
 38 struct snd_hrtimer {
 39         struct snd_timer *timer;
 40         struct hrtimer hrt;
 41         atomic_t running;
 42 };
 43 
 44 static 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         unsigned long oruns;
 49 
 50         if (!atomic_read(&stime->running))
 51                 return HRTIMER_NORESTART;
 52 
 53         oruns = hrtimer_forward_now(hrt, ns_to_ktime(t->sticks * resolution));
 54         snd_timer_interrupt(stime->timer, t->sticks * oruns);
 55 
 56         if (!atomic_read(&stime->running))
 57                 return HRTIMER_NORESTART;
 58         return HRTIMER_RESTART;
 59 }
 60 
 61 static int snd_hrtimer_open(struct snd_timer *t)
 62 {
 63         struct snd_hrtimer *stime;
 64 
 65         stime = kmalloc(sizeof(*stime), GFP_KERNEL);
 66         if (!stime)
 67                 return -ENOMEM;
 68         hrtimer_init(&stime->hrt, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 69         stime->timer = t;
 70         stime->hrt.function = snd_hrtimer_callback;
 71         atomic_set(&stime->running, 0);
 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                 hrtimer_cancel(&stime->hrt);
 82                 kfree(stime);
 83                 t->private_data = NULL;
 84         }
 85         return 0;
 86 }
 87 
 88 static int snd_hrtimer_start(struct snd_timer *t)
 89 {
 90         struct snd_hrtimer *stime = t->private_data;
 91 
 92         atomic_set(&stime->running, 0);
 93         hrtimer_cancel(&stime->hrt);
 94         hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution),
 95                       HRTIMER_MODE_REL);
 96         atomic_set(&stime->running, 1);
 97         return 0;
 98 }
 99 
100 static int snd_hrtimer_stop(struct snd_timer *t)
101 {
102         struct snd_hrtimer *stime = t->private_data;
103         atomic_set(&stime->running, 0);
104         return 0;
105 }
106 
107 static struct snd_timer_hardware hrtimer_hw = {
108         .flags =        SNDRV_TIMER_HW_AUTO | SNDRV_TIMER_HW_TASKLET,
109         .open =         snd_hrtimer_open,
110         .close =        snd_hrtimer_close,
111         .start =        snd_hrtimer_start,
112         .stop =         snd_hrtimer_stop,
113 };
114 
115 /*
116  * entry functions
117  */
118 
119 static struct snd_timer *mytimer;
120 
121 static int __init snd_hrtimer_init(void)
122 {
123         struct snd_timer *timer;
124         struct timespec tp;
125         int err;
126 
127         hrtimer_get_res(CLOCK_MONOTONIC, &tp);
128         if (tp.tv_sec > 0 || !tp.tv_nsec) {
129                 snd_printk(KERN_ERR
130                            "snd-hrtimer: Invalid resolution %u.%09u",
131                            (unsigned)tp.tv_sec, (unsigned)tp.tv_nsec);
132                 return -EINVAL;
133         }
134         resolution = tp.tv_nsec;
135 
136         /* Create a new timer and set up the fields */
137         err = snd_timer_global_new("hrtimer", SNDRV_TIMER_GLOBAL_HRTIMER,
138                                    &timer);
139         if (err < 0)
140                 return err;
141 
142         timer->module = THIS_MODULE;
143         strcpy(timer->name, "HR timer");
144         timer->hw = hrtimer_hw;
145         timer->hw.resolution = resolution;
146         timer->hw.ticks = NANO_SEC / resolution;
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);
168