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Linux/sound/core/hrtimer.c

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  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         bool in_callback;
 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         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 
 78 static 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 
 92 static 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 
109 static 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 
120 static 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 
130 static struct snd_timer_hardware hrtimer_hw = {
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 
142 static struct snd_timer *mytimer;
143 
144 static 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 
163         err = snd_timer_global_register(timer);
164         if (err < 0) {
165                 snd_timer_global_free(timer);
166                 return err;
167         }
168         mytimer = timer; /* remember this */
169 
170         return 0;
171 }
172 
173 static void __exit snd_hrtimer_exit(void)
174 {
175         if (mytimer) {
176                 snd_timer_global_free(mytimer);
177                 mytimer = NULL;
178         }
179 }
180 
181 module_init(snd_hrtimer_init);
182 module_exit(snd_hrtimer_exit);
183 

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