ALSA: Add hrtimer backend for ALSA timer interface

Added the hrtimer backend for ALSA timer interface.
It can be used for the sequencer timer source.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/hrtimer.c

@@ -0,0 +1,140 @@
+/*
+ */
+
+#include <linux/init.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 <tiwai@suse.de>");
+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;
+};
+
+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;
+	hrtimer_forward_now(hrt, ktime_set(0, t->sticks * resolution));
+	snd_timer_interrupt(stime->timer, t->sticks);
+	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.cb_mode = HRTIMER_CB_SOFTIRQ;
+	stime->hrt.function = snd_hrtimer_callback;
+	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;
+
+	hrtimer_start(&stime->hrt, ktime_set(0, t->sticks * resolution),
+		      HRTIMER_MODE_REL);
+	return 0;
+}
+
+static int snd_hrtimer_stop(struct snd_timer *t)
+{
+	struct snd_hrtimer *stime = t->private_data;
+
+	hrtimer_cancel(&stime->hrt);
+	return 0;
+}
+
+static struct snd_timer_hardware hrtimer_hw = {
+	.flags =	(SNDRV_TIMER_HW_AUTO |
+			 /*SNDRV_TIMER_HW_FIRST |*/
+			 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);