sound/core/pcm_timer.c

Source file repositories/reference/linux-study-clean/sound/core/pcm_timer.c

File Facts

System
Linux kernel
Corpus path
sound/core/pcm_timer.c
Extension
.c
Size
3052 bytes
Lines
130
Domain
Driver Families
Bucket
sound/core
Inferred role
Driver Families: implementation source
Status
source implementation candidate

Why This File Exists

Repeatable hardware-adapter layer. Deep compatibility for every driver is out of scope; this atlas records patterns, probe lifecycles, bus glue, IRQ/DMA usage, and links back to core abstractions.

Dependency Surface

Detected Declarations

Annotated Snippet

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  Digital Audio (PCM) abstract layer
 *  Copyright (c) by Jaroslav Kysela <perex@perex.cz>
 */

#include <linux/time.h>
#include <linux/gcd.h>
#include <sound/core.h>
#include <sound/pcm.h>
#include <sound/timer.h>

#include "pcm_local.h"

/*
 *  Timer functions
 */

void snd_pcm_timer_resolution_change(struct snd_pcm_substream *substream)
{
	unsigned long rate, mult, fsize, l, post;
	struct snd_pcm_runtime *runtime = substream->runtime;

	mult = 1000000000;
	rate = runtime->rate;
	if (snd_BUG_ON(!rate))
		return;
	l = gcd(mult, rate);
	mult /= l;
	rate /= l;
	fsize = runtime->period_size;
	if (snd_BUG_ON(!fsize))
		return;
	l = gcd(rate, fsize);
	rate /= l;
	fsize /= l;
	post = 1;
	while ((mult * fsize) / fsize != mult) {
		mult /= 2;
		post *= 2;
	}
	if (rate == 0) {
		pcm_err(substream->pcm,
			"pcm timer resolution out of range (rate = %u, period_size = %lu)\n",
			runtime->rate, runtime->period_size);
		runtime->timer_resolution = -1;
		return;
	}
	runtime->timer_resolution = (mult * fsize / rate) * post;
}

static unsigned long snd_pcm_timer_resolution(struct snd_timer * timer)
{
	struct snd_pcm_substream *substream;

	substream = timer->private_data;
	return substream->runtime ? substream->runtime->timer_resolution : 0;
}

static int snd_pcm_timer_start(struct snd_timer * timer)
{
	struct snd_pcm_substream *substream;

	substream = snd_timer_chip(timer);
	substream->timer_running = 1;
	return 0;
}

static int snd_pcm_timer_stop(struct snd_timer * timer)
{
	struct snd_pcm_substream *substream;

	substream = snd_timer_chip(timer);
	substream->timer_running = 0;
	return 0;
}

static const struct snd_timer_hardware snd_pcm_timer =
{
	.flags =	SNDRV_TIMER_HW_AUTO | SNDRV_TIMER_HW_SLAVE,
	.resolution =	0,
	.ticks =	1,
	.c_resolution =	snd_pcm_timer_resolution,
	.start =	snd_pcm_timer_start,
	.stop =		snd_pcm_timer_stop,
};

/*
 *  Init functions
 */

Annotation

Implementation Notes