sound/core/seq/seq_system.c

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

File Facts

System
Linux kernel
Corpus path
sound/core/seq/seq_system.c
Extension
.c
Size
5573 bytes
Lines
200
Domain
Driver Families
Bucket
sound/core
Inferred role
Driver Families: exported/initcall integration point
Status
integration 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
/*
 *   ALSA sequencer System services Client
 *   Copyright (c) 1998-1999 by Frank van de Pol <fvdpol@coil.demon.nl>
 */

#include <linux/init.h>
#include <linux/export.h>
#include <linux/slab.h>
#include <sound/core.h>
#include "seq_system.h"
#include "seq_timer.h"
#include "seq_queue.h"

/* internal client that provide system services, access to timer etc. */

/*
 * Port "Timer"
 *      - send tempo /start/stop etc. events to this port to manipulate the 
 *        queue's timer. The queue address is specified in
 *	  data.queue.queue.
 *      - this port supports subscription. The received timer events are 
 *        broadcasted to all subscribed clients. The modified tempo
 *	  value is stored on data.queue.value.
 *	  The modifier client/port is not send.
 *
 * Port "Announce"
 *      - does not receive message
 *      - supports supscription. For each client or port attaching to or 
 *        detaching from the system an announcement is send to the subscribed
 *        clients.
 *
 * Idea: the subscription mechanism might also work handy for distributing 
 * synchronisation and timing information. In this case we would ideally have
 * a list of subscribers for each type of sync (time, tick), for each timing
 * queue.
 *
 * NOTE: the queue to be started, stopped, etc. must be specified
 *	 in data.queue.addr.queue field.  queue is used only for
 *	 scheduling, and no longer referred as affected queue.
 *	 They are used only for timer broadcast (see above).
 *							-- iwai
 */


/* client id of our system client */
static int sysclient = -1;

/* port id numbers for this client */
static int announce_port = -1;

/* number of subscriptions to announce port */
static int announce_subscribed;


/* fill standard header data, source port & channel are filled in */
static int setheader(struct snd_seq_event * ev, int client, int port)
{
	if (announce_port < 0 || !announce_subscribed)
		return -ENODEV;

	memset(ev, 0, sizeof(struct snd_seq_event));

	ev->flags &= ~SNDRV_SEQ_EVENT_LENGTH_MASK;
	ev->flags |= SNDRV_SEQ_EVENT_LENGTH_FIXED;

	ev->source.client = sysclient;
	ev->source.port = announce_port;
	ev->dest.client = SNDRV_SEQ_ADDRESS_SUBSCRIBERS;

	/* fill data */
	/*ev->data.addr.queue = SNDRV_SEQ_ADDRESS_UNKNOWN;*/
	ev->data.addr.client = client;
	ev->data.addr.port = port;

	return 0;
}


/* entry points for broadcasting system events */
void snd_seq_system_broadcast(int client, int port, int type, bool atomic)
{
	struct snd_seq_event ev;
	
	if (setheader(&ev, client, port) < 0)
		return;
	ev.type = type;
	snd_seq_kernel_client_dispatch(sysclient, &ev, atomic, 0);
}
EXPORT_SYMBOL_GPL(snd_seq_system_broadcast);

Annotation

Implementation Notes