ALSA: timer - Add comments and use ns_to_ktime()
[linux-2.6.git] / 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/module.h>
23 #include <linux/moduleparam.h>
24 #include <linux/hrtimer.h>
25 #include <sound/core.h>
26 #include <sound/timer.h>
27
28 MODULE_AUTHOR("Takashi Iwai <tiwai@suse.de>");
29 MODULE_DESCRIPTION("ALSA hrtimer backend");
30 MODULE_LICENSE("GPL");
31
32 MODULE_ALIAS("snd-timer-" __stringify(SNDRV_TIMER_GLOBAL_HRTIMER));
33
34 #define NANO_SEC        1000000000UL    /* 10^9 in sec */
35 static unsigned int resolution;
36
37 struct snd_hrtimer {
38         struct snd_timer *timer;
39         struct hrtimer hrt;
40 };
41
42 static enum hrtimer_restart snd_hrtimer_callback(struct hrtimer *hrt)
43 {
44         struct snd_hrtimer *stime = container_of(hrt, struct snd_hrtimer, hrt);
45         struct snd_timer *t = stime->timer;
46         hrtimer_forward_now(hrt, ns_to_ktime(t->sticks * resolution));
47         snd_timer_interrupt(stime->timer, t->sticks);
48         return HRTIMER_RESTART;
49 }
50
51 static int snd_hrtimer_open(struct snd_timer *t)
52 {
53         struct snd_hrtimer *stime;
54
55         stime = kmalloc(sizeof(*stime), GFP_KERNEL);
56         if (!stime)
57                 return -ENOMEM;
58         hrtimer_init(&stime->hrt, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
59         stime->timer = t;
60         stime->hrt.cb_mode = HRTIMER_CB_SOFTIRQ;
61         stime->hrt.function = snd_hrtimer_callback;
62         t->private_data = stime;
63         return 0;
64 }
65
66 static int snd_hrtimer_close(struct snd_timer *t)
67 {
68         struct snd_hrtimer *stime = t->private_data;
69
70         if (stime) {
71                 hrtimer_cancel(&stime->hrt);
72                 kfree(stime);
73                 t->private_data = NULL;
74         }
75         return 0;
76 }
77
78 static int snd_hrtimer_start(struct snd_timer *t)
79 {
80         struct snd_hrtimer *stime = t->private_data;
81
82         hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution),
83                       HRTIMER_MODE_REL);
84         return 0;
85 }
86
87 static int snd_hrtimer_stop(struct snd_timer *t)
88 {
89         struct snd_hrtimer *stime = t->private_data;
90
91         hrtimer_cancel(&stime->hrt);
92         return 0;
93 }
94
95 static struct snd_timer_hardware hrtimer_hw = {
96         .flags =        (SNDRV_TIMER_HW_AUTO |
97                          /*SNDRV_TIMER_HW_FIRST |*/
98                          SNDRV_TIMER_HW_TASKLET),
99         .open =         snd_hrtimer_open,
100         .close =        snd_hrtimer_close,
101         .start =        snd_hrtimer_start,
102         .stop =         snd_hrtimer_stop,
103 };
104
105 /*
106  * entry functions
107  */
108
109 static struct snd_timer *mytimer;
110
111 static int __init snd_hrtimer_init(void)
112 {
113         struct snd_timer *timer;
114         struct timespec tp;
115         int err;
116
117         hrtimer_get_res(CLOCK_MONOTONIC, &tp);
118         if (tp.tv_sec > 0 || !tp.tv_nsec) {
119                 snd_printk(KERN_ERR
120                            "snd-hrtimer: Invalid resolution %u.%09u",
121                            (unsigned)tp.tv_sec, (unsigned)tp.tv_nsec);
122                 return -EINVAL;
123         }
124         resolution = tp.tv_nsec;
125
126         /* Create a new timer and set up the fields */
127         err = snd_timer_global_new("hrtimer", SNDRV_TIMER_GLOBAL_HRTIMER,
128                                    &timer);
129         if (err < 0)
130                 return err;
131
132         timer->module = THIS_MODULE;
133         strcpy(timer->name, "HR timer");
134         timer->hw = hrtimer_hw;
135         timer->hw.resolution = resolution;
136         timer->hw.ticks = NANO_SEC / resolution;
137
138         err = snd_timer_global_register(timer);
139         if (err < 0) {
140                 snd_timer_global_free(timer);
141                 return err;
142         }
143         mytimer = timer; /* remember this */
144
145         return 0;
146 }
147
148 static void __exit snd_hrtimer_exit(void)
149 {
150         if (mytimer) {
151                 snd_timer_global_free(mytimer);
152                 mytimer = NULL;
153         }
154 }
155
156 module_init(snd_hrtimer_init);
157 module_exit(snd_hrtimer_exit);