path: root/sound/core/init.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  Initialization routines
 *  Copyright (c) by Jaroslav Kysela <perex@perex.cz>
 */

#include <linux/init.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/file.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/ctype.h>
#include <linux/pm.h>
#include <linux/debugfs.h>
#include <linux/completion.h>
#include <linux/interrupt.h>

#include <sound/core.h>
#include <sound/control.h>
#include <sound/info.h>

/* monitor files for graceful shutdown (hotplug) */
struct snd_monitor_file {
	struct file *file;
	const struct file_operations *disconnected_f_op;
	struct list_head shutdown_list;	/* still need to shutdown */
	struct list_head list;	/* link of monitor files */
};

static DEFINE_SPINLOCK(shutdown_lock);
static LIST_HEAD(shutdown_files);

static const struct file_operations snd_shutdown_f_ops;

/* locked for registering/using */
static DECLARE_BITMAP(snd_cards_lock, SNDRV_CARDS);
static struct snd_card *snd_cards[SNDRV_CARDS];

static DEFINE_MUTEX(snd_card_mutex);

static char *slots[SNDRV_CARDS];
module_param_array(slots, charp, NULL, 0444);
MODULE_PARM_DESC(slots, "Module names assigned to the slots.");

/* return non-zero if the given index is reserved for the given
 * module via slots option
 */
static int module_slot_match(struct module *module, int idx)
{
	int match = 1;
#ifdef MODULE
	const char *s1, *s2;

	if (!module || !*module->name || !slots[idx])
		return 0;

	s1 = module->name;
	s2 = slots[idx];
	if (*s2 == '!') {
		match = 0; /* negative match */
		s2++;
	}
	/* compare module name strings
	 * hyphens are handled as equivalent with underscore
	 */
	for (;;) {
		char c1 = *s1++;
		char c2 = *s2++;
		if (c1 == '-')
			c1 = '_';
		if (c2 == '-')
			c2 = '_';
		if (c1 != c2)
			return !match;
		if (!c1)
			break;
	}
#endif /* MODULE */
	return match;
}

#if IS_ENABLED(CONFIG_SND_MIXER_OSS)
int (*snd_mixer_oss_notify_callback)(struct snd_card *card, int free_flag);
EXPORT_SYMBOL(snd_mixer_oss_notify_callback);
#endif

static int check_empty_slot(struct module *module, int slot)
{
	return !slots[slot] || !*slots[slot];
}

/* return an empty slot number (>= 0) found in the given bitmask @mask.
 * @mask == -1 == 0xffffffff means: take any free slot up to 32
 * when no slot is available, return the original @mask as is.
 */
static int get_slot_from_bitmask(int mask, int (*check)(struct module *, int),
				 struct module *module)
{
	int slot;

	for (slot = 0; slot < SNDRV_CARDS; slot++) {
		if (slot < 32 && !(mask & (1U << slot)))
			continue;
		if (!test_bit(slot, snd_cards_lock)) {
			if (check(module, slot))
				return slot; /* found */
		}
	}
	return mask; /* unchanged */
}

/* the default release callback set in snd_device_initialize() below;
 * this is just NOP for now, as almost all jobs are already done in
 * dev_free callback of snd_device chain instead.
 */
static void default_release(struct device *dev)
{
}

/**
 * snd_device_initialize - Initialize struct device for sound devices
 * @dev: device to initialize
 * @card: card to assign, optional
 */
void snd_device_initialize(struct device *dev, struct snd_card *card)
{
	device_initialize(dev);
	if (card)
		dev->parent = &card->card_dev;
	dev->class = &sound_class;
	dev->release = default_release;
}
EXPORT_SYMBOL_GPL(snd_device_initialize);

static int snd_card_init(struct snd_card *card, struct device *parent,
			 int idx, const char *xid, struct module *module,
			 size_t extra_size);
static int snd_card_do_free(struct snd_card *card);
static const struct attribute_group card_dev_attr_group;

static void release_card_device(struct device *dev)
{
	snd_card_do_free(dev_to_snd_card(dev));
}

/**
 *  snd_card_new - create and initialize a soundcard structure
 *  @parent: the parent device object
 *  @idx: card index (address) [0 ... (SNDRV_CARDS-1)]
 *  @xid: card identification (ASCII string)
 *  @module: top level module for locking
 *  @extra_size: allocate this extra size after the main soundcard structure
 *  @card_ret: the pointer to store the created card instance
 *
 *  The function allocates snd_card instance via kzalloc with the given
 *  space for the driver to use freely.  The allocated struct is stored
 *  in the given card_ret pointer.
 *
 *  Return: Zero if successful or a negative error code.
 */
int snd_card_new(struct device *parent, int idx, const char *xid,
		    struct module *module, int extra_size,
		    struct snd_card **card_ret)
{
	struct snd_card *card;
	int err;

	if (snd_BUG_ON(!card_ret))
		return -EINVAL;
	*card_ret = NULL;

	if (extra_size < 0)
		extra_size = 0;
	card = kzalloc(sizeof(*card) + extra_size, GFP_KERNEL);
	if (!card)
		return -ENOMEM;

	err = snd_card_init(card, parent, idx, xid, module, extra_size);
	if (err < 0)
		return err; /* card is freed by error handler */

	*card_ret = card;
	return 0;
}
EXPORT_SYMBOL(snd_card_new);

static void __snd_card_release(struct device *dev, void *data)
{
	snd_card_free(data);
}

/**
 * snd_devm_card_new - managed snd_card object creation
 * @parent: the parent device object
 * @idx: card index (address) [0 ... (SNDRV_CARDS-1)]
 * @xid: card identification (ASCII string)
 * @module: top level module for locking
 * @extra_size: allocate this extra size after the main soundcard structure
 * @card_ret: the pointer to store the created card instance
 *
 * This function works like snd_card_new() but manages the allocated resource
 * via devres, i.e. you don't need to free explicitly.
 *
 * When a snd_card object is created with this function and registered via
 * snd_card_register(), the very first devres action to call snd_card_free()
 * is added automatically.  In that way, the resource disconnection is assured
 * at first, then released in the expected order.
 *
 * If an error happens at the probe before snd_card_register() is called and
 * there have been other devres resources, you'd need to free the card manually
 * via snd_card_free() call in the error; otherwise it may lead to UAF due to
 * devres call orders.  You can use snd_card_free_on_error() helper for
 * handling it more easily.
 *
 * Return: zero if successful, or a negative error code
 */
int snd_devm_card_new(struct device *parent, int idx, const char *xid,
		      struct module *module, size_t extra_size,
		      struct snd_card **card_ret)
{
	struct snd_card *card;
	int err;

	*card_ret = NULL;
	card = devres_alloc(__snd_card_release, sizeof(*card) + extra_size,
			    GFP_KERNEL);
	if (!card)
		return -ENOMEM;
	card->managed = true;
	err = snd_card_init(card, parent, idx, xid, module, extra_size);
	if (err < 0) {
		devres_free(card); /* in managed mode, we need to free manually */
		return err;
	}

	devres_add(parent, card);
	*card_ret = card;
	return 0;
}
EXPORT_SYMBOL_GPL(snd_devm_card_new);

/**
 * snd_card_free_on_error - a small helper for handling devm probe errors
 * @dev: the managed device object
 * @ret: the return code from the probe callback
 *
 * This function handles the explicit snd_card_free() call at the error from
 * the probe callback.  It's just a small helper for simplifying the error
 * handling with the managed devices.
 *
 * Return: zero if successful, or a negative error code
 */
int snd_card_free_on_error(struct device *dev, int ret)
{
	struct snd_card *card;

	if (!ret)
		return 0;
	card = devres_find(dev, __snd_card_release, NULL, NULL);
	if (card)
		snd_card_free(card);
	return ret;
}
EXPORT_SYMBOL_GPL(snd_card_free_on_error);

static int snd_card_init(struct snd_card *card, struct device *parent,
			 int idx, const char *xid, struct module *module,
			 size_t extra_size)
{
	int err;
#ifdef CONFIG_SND_DEBUG
	char name[8];
#endif

	if (extra_size > 0)
		card->private_data = (char *)card + sizeof(struct snd_card);
	if (xid)
		strscpy(card->id, xid, sizeof(card->id));
	err = 0;
	mutex_lock(&snd_card_mutex);
	if (idx < 0) /* first check the matching module-name slot */
		idx = get_slot_from_bitmask(idx, module_slot_match, module);
	if (idx < 0) /* if not matched, assign an empty slot */
		idx = get_slot_from_bitmask(idx, check_empty_slot, module);
	if (idx < 0)
		err = -ENODEV;
	else if (idx < snd_ecards_limit) {
		if (test_bit(idx, snd_cards_lock))
			err = -EBUSY;	/* invalid */
	} else if (idx >= SNDRV_CARDS)
		err = -ENODEV;
	if (err < 0) {
		mutex_unlock(&snd_card_mutex);
		dev_err(parent, "cannot find the slot for index %d (range 0-%i), error: %d\n",
			 idx, snd_ecards_limit - 1, err);
		if (!card->managed)
			kfree(card); /* manually free here, as no destructor called */
		return err;
	}
	set_bit(idx, snd_cards_lock);		/* lock it */
	if (idx >= snd_ecards_limit)
		snd_ecards_limit = idx + 1; /* increase the limit */
	mutex_unlock(&snd_card_mutex);
	card->dev = parent;
	card->number = idx;
#ifdef MODULE
	WARN_ON(!module);
	card->module = module;
#endif
	INIT_LIST_HEAD(&card->devices);
	init_rwsem(&card->controls_rwsem);
	rwlock_init(&card->ctl_files_rwlock);
	INIT_LIST_HEAD(&card->controls);
	INIT_LIST_HEAD(&card->ctl_files);
#ifdef CONFIG_SND_CTL_FAST_LOOKUP
	xa_init(&card->ctl_numids);
	xa_init(&card->ctl_hash);
#endif
	spin_lock_init(&card->files_lock);
	INIT_LIST_HEAD(&card->files_list);
	mutex_init(&card->memory_mutex);
#ifdef CONFIG_PM
	init_waitqueue_head(&card->power_sleep);
	init_waitqueue_head(&card->power_ref_sleep);
	atomic_set(&card->power_ref, 0);
#endif
	init_waitqueue_head(&card->remove_sleep);
	card->sync_irq = -1;

	device_initialize(&card->card_dev);
	card->card_dev.parent = parent;
	card->card_dev.class = &sound_class;
	card->card_dev.release = release_card_device;
	card->card_dev.groups = card->dev_groups;
	card->dev_groups[0] = &card_dev_attr_group;
	err = kobject_set_name(&card->card_dev.kobj, "card%d", idx);
	if (err < 0)
		goto __error;

	snprintf(card->irq_descr, sizeof(card->irq_descr), "%s:%s",
		 dev_driver_string(card->dev), dev_name(&card->card_dev));

	/* the control interface cannot be accessed from the user space until */
	/* snd_cards_bitmask and snd_cards are set with snd_card_register */
	err = snd_ctl_create(card);
	if (err < 0) {
		dev_err(parent, "unable to register control minors\n");
		goto __error;
	}
	err = snd_info_card_create(card);
	if (err < 0) {
		dev_err(parent, "unable to create card info\n");
		goto __error_ctl;
	}

#ifdef CONFIG_SND_DEBUG
	sprintf(name, "card%d", idx);
	card->debugfs_root = debugfs_create_dir(name, sound_debugfs_root);
#endif
	return 0;

      __error_ctl:
	snd_device_free_all(card);
      __error:
	put_device(&card->card_dev);
  	return err;
}

/**
 * snd_card_ref - Get the card object from the index
 * @idx: the card index
 *
 * Returns a card object corresponding to the given index or NULL if not found.
 * Release the object via snd_card_unref().
 *
 * Return: a card object or NULL
 */
struct snd_card *snd_card_ref(int idx)
{
	struct snd_card *card;

	mutex_lock(&snd_card_mutex);
	card = snd_cards[idx];
	if (card)
		get_device(&card->card_dev);
	mutex_unlock(&snd_card_mutex);
	return card;
}
EXPORT_SYMBOL_GPL(snd_card_ref);

/* return non-zero if a card is already locked */
int snd_card_locked(int card)
{
	int locked;

	mutex_lock(&snd_card_mutex);
	locked = test_bit(card, snd_cards_lock);
	mutex_unlock(&snd_card_mutex);
	return locked;
}

static loff_t snd_disconnect_llseek(struct file *file, loff_t offset, int orig)
{
	return -ENODEV;
}

static ssize_t snd_disconnect_read(struct file *file, char __user *buf,
				   size_t count, loff_t *offset)
{
	return -ENODEV;
}

static ssize_t snd_disconnect_write(struct file *file, const char __user *buf,
				    size_t count, loff_t *offset)
{
	return -ENODEV;
}

static int snd_disconnect_release(struct inode *inode, struct file *file)
{
	struct snd_monitor_file *df = NULL, *_df;

	spin_lock(&shutdown_lock);
	list_for_each_entry(_df, &shutdown_files, shutdown_list) {
		if (_df->file == file) {
			df = _df;
			list_del_init(&df->shutdown_list);
			break;
		}
	}
	spin_unlock(&shutdown_lock);

	if (likely(df)) {
		if ((file->f_flags & FASYNC) && df->disconnected_f_op->fasync)
			df->disconnected_f_op->fasync(-1, file, 0);
		return df->disconnected_f_op->release(inode, file);
	}

	panic("%s(%p, %p) failed!", __func__, inode, file);
}

static __poll_t snd_disconnect_poll(struct file * file, poll_table * wait)
{
	return EPOLLERR | EPOLLNVAL;
}

static long snd_disconnect_ioctl(struct file *file,
				 unsigned int cmd, unsigned long arg)
{
	return -ENODEV;
}

static int snd_disconnect_mmap(struct file *file, struct vm_area_struct *vma)
{
	return -ENODEV;
}

static int snd_disconnect_fasync(int fd, struct file *file, int on)
{
	return -ENODEV;
}

static const struct file_operations snd_shutdown_f_ops =
{
	.owner = 	THIS_MODULE,
	.llseek =	snd_disconnect_llseek,
	.read = 	snd_disconnect_read,
	.write =	snd_disconnect_write,
	.release =	snd_disconnect_release,
	.poll =		snd_disconnect_poll,
	.unlocked_ioctl = snd_disconnect_ioctl,
#ifdef CONFIG_COMPAT
	.compat_ioctl = snd_disconnect_ioctl,
#endif
	.mmap =		snd_disconnect_mmap,
	.fasync =	snd_disconnect_fasync
};

/**
 *  snd_card_disconnect - disconnect all APIs from the file-operations (user space)
 *  @card: soundcard structure
 *
 *  Disconnects all APIs from the file-operations (user space).
 *
 *  Return: Zero, otherwise a negative error code.
 *
 *  Note: The current implementation replaces all active file->f_op with special
 *        dummy file operations (they do nothing except release).
 */
void snd_card_disconnect(struct snd_card *card)
{
	struct snd_monitor_file *mfile;

	if (!card)
		return;

	spin_lock(&card->files_lock);
	if (card->shutdown) {
		spin_unlock(&card->files_lock);
		return;
	}
	card->shutdown = 1;

	/* replace file->f_op with special dummy operations */
	list_for_each_entry(mfile, &card->files_list, list) {
		/* it's critical part, use endless loop */
		/* we have no room to fail */
		mfile->disconnected_f_op = mfile->file->f_op;

		spin_lock(&shutdown_lock);
		list_add(&mfile->shutdown_list, &shutdown_files);
		spin_unlock(&shutdown_lock);

		mfile->file->f_op = &snd_shutdown_f_ops;
		fops_get(mfile->file->f_op);
	}
	spin_unlock(&card->files_lock);	

	/* notify all connected devices about disconnection */
	/* at this point, they cannot respond to any calls except release() */

#if IS_ENABLED(CONFIG_SND_MIXER_OSS)
	if (snd_mixer_oss_notify_callback)
		snd_mixer_oss_notify_callback(card, SND_MIXER_OSS_NOTIFY_DISCONNECT);
#endif

	/* notify all devices that we are disconnected */
	snd_device_disconnect_all(card);

	if (card->sync_irq > 0)
		synchronize_irq(card->sync_irq);

	snd_info_card_disconnect(card);
	if (card->registered) {
		device_del(&card->card_dev);
		card->registered = false;
	}

	/* disable fops (user space) operations for ALSA API */
	mutex_lock(&snd_card_mutex);
	snd_cards[card->number] = NULL;
	clear_bit(card->number, snd_cards_lock);
	mutex_unlock(&snd_card_mutex);

#ifdef CONFIG_PM
	wake_up(&card->power_sleep);
	snd_power_sync_ref(card);
#endif
}
EXPORT_SYMBOL(snd_card_disconnect);

/**
 * snd_card_disconnect_sync - disconnect card and wait until files get closed
 * @card: card object to disconnect
 *
 * This calls snd_card_disconnect() for disconnecting all belonging components
 * and waits until all pending files get closed.
 * It assures that all accesses from user-space finished so that the driver
 * can release its resources gracefully.
 */
void snd_card_disconnect_sync(struct snd_card *card)
{
	snd_card_disconnect(card);

	spin_lock_irq(&card->files_lock);
	wait_event_lock_irq(card->remove_sleep,
			    list_empty(&card->files_list),
			    card->files_lock);
	spin_unlock_irq(&card->files_lock);
}
EXPORT_SYMBOL_GPL(snd_card_disconnect_sync);

static int snd_card_do_free(struct snd_card *card)
{
	card->releasing = true;
#if IS_ENABLED(CONFIG_SND_MIXER_OSS)
	if (snd_mixer_oss_notify_callback)
		snd_mixer_oss_notify_callback(card, SND_MIXER_OSS_NOTIFY_FREE);
#endif
	snd_device_free_all(card);
	if (card->private_free)
		card->private_free(card);
	if (snd_info_card_free(card) < 0) {
		dev_warn(card->dev, "unable to free card info\n");
		/* Not fatal error */
	}
#ifdef CONFIG_SND_DEBUG
	debugfs_remove(card->debugfs_root);
	card->debugfs_root = NULL;
#endif
	if (card->release_completion)
		complete(card->release_completion);
	if (!card->managed)
		kfree(card);
	return 0;
}

/**
 * snd_card_free_when_closed - Disconnect the card, free it later eventually
 * @card: soundcard structure
 *
 * Unlike snd_card_free(), this function doesn't try to release the card
 * resource immediately, but tries to disconnect at first.  When the card
 * is still in use, the function returns before freeing the resources.
 * The card resources will be freed when the refcount gets to zero.
 *
 * Return: zero if successful, or a negative error code
 */
void snd_card_free_when_closed(struct snd_card *card)
{
	if (!card)
		return;

	snd_card_disconnect(card);
	put_device(&card->card_dev);
	return;
}
EXPORT_SYMBOL(snd_card_free_when_closed);

/**
 * snd_card_free - frees given soundcard structure
 * @card: soundcard structure
 *
 * This function releases the soundcard structure and the all assigned
 * devices automatically.  That is, you don't have to release the devices
 * by yourself.
 *
 * This function waits until the all resources are properly released.
 *
 * Return: Zero. Frees all associated devices and frees the control
 * interface associated to given soundcard.
 */
void snd_card_free(struct snd_card *card)
{
	DECLARE_COMPLETION_ONSTACK(released);

	/* The call of snd_card_free() is allowed from various code paths;
	 * a manual call from the driver and the call via devres_free, and
	 * we need to avoid double-free. Moreover, the release via devres
	 * may call snd_card_free() twice due to its nature, we need to have
	 * the check here at the beginning.
	 */
	if (card->releasing)
		return;

	card->release_completion = &released;
	snd_card_free_when_closed(card);

	/* wait, until all devices are ready for the free operation */
	wait_for_completion(&released);
}
EXPORT_SYMBOL(snd_card_free);

/* retrieve the last word of shortname or longname */
static const char *retrieve_id_from_card_name(const char *name)
{
	const char *spos = name;

	while (*name) {
		if (isspace(*name) && isalnum(name[1]))
			spos = name + 1;
		name++;
	}
	return spos;
}

/* return true if the given id string doesn't conflict any other card ids */
static bool card_id_ok(struct snd_card *card, const char *id)
{
	int i;
	if (!snd_info_check_reserved_words(id))
		return false;
	for (i = 0; i < snd_ecards_limit; i++) {
		if (snd_cards[i] && snd_cards[i] != card &&
		    !strcmp(snd_cards[i]->id, id))
			return false;
	}
	return true;
}

/* copy to card->id only with valid letters from nid */
static void copy_valid_id_string(struct snd_card *card, const char *src,
				 const char *nid)
{
	char *id = card->id;

	while (*nid && !isalnum(*nid))
		nid++;
	if (isdigit(*nid))
		*id++ = isalpha(*src) ? *src : 'D';
	while (*nid && (size_t)(id - card->id) < sizeof(card->id) - 1) {
		if (isalnum(*nid))
			*id++ = *nid;
		nid++;
	}
	*id = 0;
}

/* Set card->id from the given string
 * If the string conflicts with other ids, add a suffix to make it unique.
 */
static void snd_card_set_id_no_lock(struct snd_card *card, const char *src,
				    const char *nid)
{
	int len, loops;
	bool is_default = false;
	char *id;
	
	copy_valid_id_string(card, src, nid);
	id = card->id;

 again:
	/* use "Default" for obviously invalid strings
	 * ("card" conflicts with proc directories)
	 */
	if (!*id || !strncmp(id, "card", 4)) {
		strcpy(id, "Default");
		is_default = true;
	}

	len = strlen(id);
	for (loops = 0; loops < SNDRV_CARDS; loops++) {
		char *spos;
		char sfxstr[5]; /* "_012" */
		int sfxlen;

		if (card_id_ok(card, id))
			return; /* OK */

		/* Add _XYZ suffix */
		sprintf(sfxstr, "_%X", loops + 1);
		sfxlen = strlen(sfxstr);
		if (len + sfxlen >= sizeof(card->id))
			spos = id + sizeof(card->id) - sfxlen - 1;
		else
			spos = id + len;
		strcpy(spos, sfxstr);
	}
	/* fallback to the default id */
	if (!is_default) {
		*id = 0;
		goto again;
	}
	/* last resort... */
	dev_err(card->dev, "unable to set card id (%s)\n", id);
	if (card->proc_root->name)
		strscpy(card->id, card->proc_root->name, sizeof(card->id));
}

/**
 *  snd_card_set_id - set card identification name
 *  @card: soundcard structure
 *  @nid: new identification string
 *
 *  This function sets the card identification and checks for name
 *  collisions.
 */
void snd_card_set_id(struct snd_card *card, const char *nid)
{
	/* check if user specified own card->id */
	if (card->id[0] != '\0')
		return;
	mutex_lock(&snd_card_mutex);
	snd_card_set_id_no_lock(card, nid, nid);
	mutex_unlock(&snd_card_mutex);
}
EXPORT_SYMBOL(snd_card_set_id);

static ssize_t id_show(struct device *dev,
		       struct device_attribute *attr, char *buf)
{
	struct snd_card *card = container_of(dev, struct snd_card, card_dev);
	return sysfs_emit(buf, "%s\n", card->id);
}

static ssize_t id_store(struct device *dev, struct device_attribute *attr,
			const char *buf, size_t count)
{
	struct snd_card *card = container_of(dev, struct snd_card, card_dev);
	char buf1[sizeof(card->id)];
	size_t copy = count > sizeof(card->id) - 1 ?
					sizeof(card->id) - 1 : count;
	size_t idx;
	int c;

	for (idx = 0; idx < copy; idx++) {
		c = buf[idx];
		if (!isalnum(c) && c != '_' && c != '-')
			return -EINVAL;
	}
	memcpy(buf1, buf, copy);
	buf1[copy] = '\0';
	mutex_lock(&snd_card_mutex);
	if (!card_id_ok(NULL, buf1)) {
		mutex_unlock(&snd_card_mutex);
		return -EEXIST;
	}
	strcpy(card->id, buf1);
	snd_info_card_id_change(card);
	mutex_unlock(&snd_card_mutex);

	return count;
}

static DEVICE_ATTR_RW(id);

static ssize_t number_show(struct device *dev,
			   struct device_attribute *attr, char *buf)
{
	struct snd_card *card = container_of(dev, struct snd_card, card_dev);
	return sysfs_emit(buf, "%i\n", card->number);
}

static DEVICE_ATTR_RO(number);

static struct attribute *card_dev_attrs[] = {
	&dev_attr_id.attr,
	&dev_attr_number.attr,
	NULL
};

static const struct attribute_group card_dev_attr_group = {
	.attrs	= card_dev_attrs,
};

/**
 * snd_card_add_dev_attr - Append a new sysfs attribute group to card
 * @card: card instance
 * @group: attribute group to append
 *
 * Return: zero if successful, or a negative error code
 */
int snd_card_add_dev_attr(struct snd_card *card,
			  const struct attribute_group *group)
{
	int i;

	/* loop for (arraysize-1) here to keep NULL at the last entry */
	for (i = 0; i < ARRAY_SIZE(card->dev_groups) - 1; i++) {
		if (!card->dev_groups[i]) {
			card->dev_groups[i] = group;
			return 0;
		}
	}

	dev_err(card->dev, "Too many groups assigned\n");
	return -ENOSPC;
}
EXPORT_SYMBOL_GPL(snd_card_add_dev_attr);

static void trigger_card_free(void *data)
{
	snd_card_free(data);
}

/**
 *  snd_card_register - register the soundcard
 *  @card: soundcard structure
 *
 *  This function registers all the devices assigned to the soundcard.
 *  Until calling this, the ALSA control interface is blocked from the
 *  external accesses.  Thus, you should call this function at the end
 *  of the initialization of the card.
 *
 *  Return: Zero otherwise a negative error code if the registration failed.
 */
int snd_card_register(struct snd_card *card)
{
	int err;

	if (snd_BUG_ON(!card))
		return -EINVAL;

	if (!card->registered) {
		err = device_add(&card->card_dev);
		if (err < 0)
			return err;
		card->registered = true;
	} else {
		if (card->managed)
			devm_remove_action(card->dev, trigger_card_free, card);
	}

	if (card->managed) {
		err = devm_add_action(card->dev, trigger_card_free, card);
		if (err < 0)
			return err;
	}

	err = snd_device_register_all(card);
	if (err < 0)
		return err;
	mutex_lock(&snd_card_mutex);
	if (snd_cards[card->number]) {
		/* already registered */
		mutex_unlock(&snd_card_mutex);
		return snd_info_card_register(card); /* register pending info */
	}
	if (*card->id) {
		/* make a unique id name from the given string */
		char tmpid[sizeof(card->id)];
		memcpy(tmpid, card->id, sizeof(card->id));
		snd_card_set_id_no_lock(card, tmpid, tmpid);
	} else {
		/* create an id from either shortname or longname */
		const char *src;
		src = *card->shortname ? card->shortname : card->longname;
		snd_card_set_id_no_lock(card, src,
					retrieve_id_from_card_name(src));
	}
	snd_cards[card->number] = card;
	mutex_unlock(&snd_card_mutex);
	err = snd_info_card_register(card);
	if (err < 0)
		return err;

#if IS_ENABLED(CONFIG_SND_MIXER_OSS)
	if (snd_mixer_oss_notify_callback)
		snd_mixer_oss_notify_callback(card, SND_MIXER_OSS_NOTIFY_REGISTER);
#endif
	return 0;
}
EXPORT_SYMBOL(snd_card_register);

#ifdef CONFIG_SND_PROC_FS
static void snd_card_info_read(struct snd_info_entry *entry,
			       struct snd_info_buffer *buffer)
{
	int idx, count;
	struct snd_card *card;

	for (idx = count = 0; idx < SNDRV_CARDS; idx++) {
		mutex_lock(&snd_card_mutex);
		card = snd_cards[idx];
		if (card) {
			count++;
			snd_iprintf(buffer, "%2i [%-15s]: %s - %s\n",
					idx,
					card->id,
					card->driver,
					card->shortname);
			snd_iprintf(buffer, "                      %s\n",
					card->longname);
		}
		mutex_unlock(&snd_card_mutex);
	}
	if (!count)
		snd_iprintf(buffer, "--- no soundcards ---\n");
}

#ifdef CONFIG_SND_OSSEMUL
void snd_card_info_read_oss(struct snd_info_buffer *buffer)
{
	int idx, count;
	struct snd_card *card;

	for (idx = count = 0; idx < SNDRV_CARDS; idx++) {
		mutex_lock(&snd_card_mutex);
		card = snd_cards[idx];
		if (card) {
			count++;
			snd_iprintf(buffer, "%s\n", card->longname);
		}
		mutex_unlock(&snd_card_mutex);
	}
	if (!count) {
		snd_iprintf(buffer, "--- no soundcards ---\n");
	}
}

#endif

#ifdef MODULE
static void snd_card_module_info_read(struct snd_info_entry *entry,
				      struct snd_info_buffer *buffer)
{
	int idx;
	struct snd_card *card;

	for (idx = 0; idx < SNDRV_CARDS; idx++) {
		mutex_lock(&snd_card_mutex);
		card = snd_cards[idx];
		if (card)
			snd_iprintf(buffer, "%2i %s\n",
				    idx, card->module->name);
		mutex_unlock(&snd_card_mutex);
	}
}
#endif

int __init snd_card_info_init(void)
{
	struct snd_info_entry *entry;

	entry = snd_info_create_module_entry(THIS_MODULE, "cards", NULL);
	if (! entry)
		return -ENOMEM;
	entry->c.text.read = snd_card_info_read;
	if (snd_info_register(entry) < 0)
		return -ENOMEM; /* freed in error path */

#ifdef MODULE
	entry = snd_info_create_module_entry(THIS_MODULE, "modules", NULL);
	if (!entry)
		return -ENOMEM;
	entry->c.text.read = snd_card_module_info_read;
	if (snd_info_register(entry) < 0)
		return -ENOMEM; /* freed in error path */
#endif

	return 0;
}
#endif /* CONFIG_SND_PROC_FS */

/**
 *  snd_component_add - add a component string
 *  @card: soundcard structure
 *  @component: the component id string
 *
 *  This function adds the component id string to the supported list.
 *  The component can be referred from the alsa-lib.
 *
 *  Return: Zero otherwise a negative error code.
 */
  
int snd_component_add(struct snd_card *card, const char *component)
{
	char *ptr;
	int len = strlen(component);

	ptr = strstr(card->components, component);
	if (ptr != NULL) {
		if (ptr[len] == '\0' || ptr[len] == ' ')	/* already there */
			return 1;
	}
	if (strlen(card->components) + 1 + len + 1 > sizeof(card->components)) {
		snd_BUG();
		return -ENOMEM;
	}
	if (card->components[0] != '\0')
		strcat(card->components, " ");
	strcat(card->components, component);
	return 0;
}
EXPORT_SYMBOL(snd_component_add);

/**
 *  snd_card_file_add - add the file to the file list of the card
 *  @card: soundcard structure
 *  @file: file pointer
 *
 *  This function adds the file to the file linked-list of the card.
 *  This linked-list is used to keep tracking the connection state,
 *  and to avoid the release of busy resources by hotplug.
 *
 *  Return: zero or a negative error code.
 */
int snd_card_file_add(struct snd_card *card, struct file *file)
{
	struct snd_monitor_file *mfile;

	mfile = kmalloc(sizeof(*mfile), GFP_KERNEL);
	if (mfile == NULL)
		return -ENOMEM;
	mfile->file = file;
	mfile->disconnected_f_op = NULL;
	INIT_LIST_HEAD(&mfile->shutdown_list);
	spin_lock(&card->files_lock);
	if (card->shutdown) {
		spin_unlock(&card->files_lock);
		kfree(mfile);
		return -ENODEV;
	}
	list_add(&mfile->list, &card->files_list);
	get_device(&card->card_dev);
	spin_unlock(&card->files_lock);
	return 0;
}
EXPORT_SYMBOL(snd_card_file_add);

/**
 *  snd_card_file_remove - remove the file from the file list
 *  @card: soundcard structure
 *  @file: file pointer
 *
 *  This function removes the file formerly added to the card via
 *  snd_card_file_add() function.
 *  If all files are removed and snd_card_free_when_closed() was
 *  called beforehand, it processes the pending release of
 *  resources.
 *
 *  Return: Zero or a negative error code.
 */
int snd_card_file_remove(struct snd_card *card, struct file *file)
{
	struct snd_monitor_file *mfile, *found = NULL;

	spin_lock(&card->files_lock);
	list_for_each_entry(mfile, &card->files_list, list) {
		if (mfile->file == file) {
			list_del(&mfile->list);
			spin_lock(&shutdown_lock);
			list_del(&mfile->shutdown_list);
			spin_unlock(&shutdown_lock);
			if (mfile->disconnected_f_op)
				fops_put(mfile->disconnected_f_op);
			found = mfile;
			break;
		}
	}
	if (list_empty(&card->files_list))
		wake_up_all(&card->remove_sleep);
	spin_unlock(&card->files_lock);
	if (!found) {
		dev_err(card->dev, "card file remove problem (%p)\n", file);
		return -ENOENT;
	}
	kfree(found);
	put_device(&card->card_dev);
	return 0;
}
EXPORT_SYMBOL(snd_card_file_remove);

#ifdef CONFIG_PM
/**
 * snd_power_ref_and_wait - wait until the card gets powered up
 * @card: soundcard structure
 *
 * Take the power_ref reference count of the given card, and
 * wait until the card gets powered up to SNDRV_CTL_POWER_D0 state.
 * The refcount is down again while sleeping until power-up, hence this
 * function can be used for syncing the floating control ops accesses,
 * typically around calling control ops.
 *
 * The caller needs to pull down the refcount via snd_power_unref() later
 * no matter whether the error is returned from this function or not.
 *
 * Return: Zero if successful, or a negative error code.
 */
int snd_power_ref_and_wait(struct snd_card *card)
{
	snd_power_ref(card);
	if (snd_power_get_state(card) == SNDRV_CTL_POWER_D0)
		return 0;
	wait_event_cmd(card->power_sleep,
		       card->shutdown ||
		       snd_power_get_state(card) == SNDRV_CTL_POWER_D0,
		       snd_power_unref(card), snd_power_ref(card));
	return card->shutdown ? -ENODEV : 0;
}
EXPORT_SYMBOL_GPL(snd_power_ref_and_wait);

/**
 * snd_power_wait - wait until the card gets powered up (old form)
 * @card: soundcard structure
 *
 * Wait until the card gets powered up to SNDRV_CTL_POWER_D0 state.
 *
 * Return: Zero if successful, or a negative error code.
 */
int snd_power_wait(struct snd_card *card)
{
	int ret;

	ret = snd_power_ref_and_wait(card);
	snd_power_unref(card);
	return ret;
}
EXPORT_SYMBOL(snd_power_wait);
#endif /* CONFIG_PM */