hrtimer.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * ALSA timer back-end using hrtimer
  4 * Copyright (C) 2008 Takashi Iwai
  5 */
  6
  7#include <linux/init.h>
  8#include <linux/slab.h>
  9#include <linux/string.h>
 10#include <linux/module.h>
 11#include <linux/moduleparam.h>
 12#include <linux/hrtimer.h>
 13#include <sound/core.h>
 14#include <sound/timer.h>
 15
 16MODULE_AUTHOR("Takashi Iwai <tiwai@suse.de>");
 17MODULE_DESCRIPTION("ALSA hrtimer backend");
 18MODULE_LICENSE("GPL");
 19
 20MODULE_ALIAS("snd-timer-" __stringify(SNDRV_TIMER_GLOBAL_HRTIMER));
 21
 22#define NANO_SEC	1000000000UL	/* 10^9 in sec */
 23static unsigned int resolution;
 24
 25struct snd_hrtimer {
 26	struct snd_timer *timer;
 27	struct hrtimer hrt;
 28	bool in_callback;
 29};
 30
 31static enum hrtimer_restart snd_hrtimer_callback(struct hrtimer *hrt)
 32{
 33	struct snd_hrtimer *stime = container_of(hrt, struct snd_hrtimer, hrt);
 34	struct snd_timer *t = stime->timer;
 35	ktime_t delta;
 36	unsigned long ticks;
 37	enum hrtimer_restart ret = HRTIMER_NORESTART;
 38
 39	scoped_guard(spinlock, &t->lock) {
 40		if (!t->running)
 41			return HRTIMER_NORESTART; /* fast path */
 42		stime->in_callback = true;
 43		ticks = t->sticks;
 44	}
 45
 46	/* calculate the drift */
 47	delta = ktime_sub(hrtimer_cb_get_time(hrt), hrtimer_get_expires(hrt));
 48	if (delta > 0)
 49		ticks += ktime_divns(delta, ticks * resolution);
 50
 51	snd_timer_interrupt(stime->timer, ticks);
 52
 53	guard(spinlock)(&t->lock);
 54	if (t->running) {
 55		hrtimer_add_expires_ns(hrt, t->sticks * resolution);
 56		ret = HRTIMER_RESTART;
 57	}
 58
 59	stime->in_callback = false;
 60	return ret;
 61}
 62
 63static int snd_hrtimer_open(struct snd_timer *t)
 64{
 65	struct snd_hrtimer *stime;
 66
 67	stime = kzalloc(sizeof(*stime), GFP_KERNEL);
 68	if (!stime)
 69		return -ENOMEM;
 70	stime->timer = t;
 71	hrtimer_setup(&stime->hrt, snd_hrtimer_callback, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 72	t->private_data = stime;
 73	return 0;
 74}
 75
 76static int snd_hrtimer_close(struct snd_timer *t)
 77{
 78	struct snd_hrtimer *stime = t->private_data;
 79
 80	if (stime) {
 81		scoped_guard(spinlock_irq, &t->lock) {
 82			t->running = 0; /* just to be sure */
 83			stime->in_callback = 1; /* skip start/stop */
 84		}
 85
 86		hrtimer_cancel(&stime->hrt);
 87		kfree(stime);
 88		t->private_data = NULL;
 89	}
 90	return 0;
 91}
 92
 93static int snd_hrtimer_start(struct snd_timer *t)
 94{
 95	struct snd_hrtimer *stime = t->private_data;
 96
 97	if (stime->in_callback)
 98		return 0;
 99	hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution),
100		      HRTIMER_MODE_REL);
101	return 0;
102}
103
104static int snd_hrtimer_stop(struct snd_timer *t)
105{
106	struct snd_hrtimer *stime = t->private_data;
107
108	if (stime->in_callback)
109		return 0;
110	hrtimer_try_to_cancel(&stime->hrt);
111	return 0;
112}
113
114static const struct snd_timer_hardware hrtimer_hw __initconst = {
115	.flags =	SNDRV_TIMER_HW_AUTO | SNDRV_TIMER_HW_WORK,
116	.open =		snd_hrtimer_open,
117	.close =	snd_hrtimer_close,
118	.start =	snd_hrtimer_start,
119	.stop =		snd_hrtimer_stop,
120};
121
122/*
123 * entry functions
124 */
125
126static struct snd_timer *mytimer;
127
128static int __init snd_hrtimer_init(void)
129{
130	struct snd_timer *timer;
131	int err;
132
133	resolution = hrtimer_resolution;
134
135	/* Create a new timer and set up the fields */
136	err = snd_timer_global_new("hrtimer", SNDRV_TIMER_GLOBAL_HRTIMER,
137				   &timer);
138	if (err < 0)
139		return err;
140
141	timer->module = THIS_MODULE;
142	strscpy(timer->name, "HR timer");
143	timer->hw = hrtimer_hw;
144	timer->hw.resolution = resolution;
145	timer->hw.ticks = NANO_SEC / resolution;
146	timer->max_instances = 100; /* lower the limit */
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
158static void __exit snd_hrtimer_exit(void)
159{
160	if (mytimer) {
161		snd_timer_global_free(mytimer);
162		mytimer = NULL;
163	}
164}
165
166module_init(snd_hrtimer_init);
167module_exit(snd_hrtimer_exit);