sound/core/vmaster.c - third_party/kernel - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * Virtual master and follower controls
  *
  *  Copyright (c) 2008 by Takashi Iwai <tiwai@suse.de>
  */

 #include <linux/slab.h>
 #include <linux/export.h>
 #include <sound/core.h>
 #include <sound/control.h>
 #include <sound/tlv.h>

 /*
  * a subset of information returned via ctl info callback
  */
 struct link_ctl_info {
 	snd_ctl_elem_type_t type; /* value type */
 	int count;		/* item count */
 	int min_val, max_val;	/* min, max values */
 };

 /*
  * link master - this contains a list of follower controls that are
  * identical types, i.e. info returns the same value type and value
  * ranges, but may have different number of counts.
  *
  * The master control is so far only mono volume/switch for simplicity.
  * The same value will be applied to all followers.
  */
 struct link_master {
 	struct list_head followers;
 	struct link_ctl_info info;
 	int val;		/* the master value */
 	unsigned int tlv[4];
 	void (*hook)(void *private_data, int);
 	void *hook_private_data;
 };

 /*
  * link follower - this contains a follower control element
  *
  * It fakes the control callbacks with additional attenuation by the
  * master control.  A follower may have either one or two channels.
  */

 struct link_follower {
 	struct list_head list;
 	struct link_master *master;
 	struct link_ctl_info info;
 	int vals[2];		/* current values */
 	unsigned int flags;
 	struct snd_kcontrol *kctl; /* original kcontrol pointer */
 	struct snd_kcontrol follower; /* the copy of original control entry */
 };

 static int follower_update(struct link_follower *follower)
 {
 	struct snd_ctl_elem_value *uctl;
 	int err, ch;

 	uctl = kzalloc(sizeof(*uctl), GFP_KERNEL);
 	if (!uctl)
 		return -ENOMEM;
 	uctl->id = follower->follower.id;
 	err = follower->follower.get(&follower->follower, uctl);
 	if (err < 0)
 		goto error;
 	for (ch = 0; ch < follower->info.count; ch++)
 		follower->vals[ch] = uctl->value.integer.value[ch];
  error:
 	kfree(uctl);
 	return err < 0 ? err : 0;
 }

 /* get the follower ctl info and save the initial values */
 static int follower_init(struct link_follower *follower)
 {
 	struct snd_ctl_elem_info *uinfo;
 	int err;

 	if (follower->info.count) {
 		/* already initialized */
 		if (follower->flags & SND_CTL_FOLLOWER_NEED_UPDATE)
 			return follower_update(follower);
 		return 0;
 	}

 	uinfo = kmalloc(sizeof(*uinfo), GFP_KERNEL);
 	if (!uinfo)
 		return -ENOMEM;
 	uinfo->id = follower->follower.id;
 	err = follower->follower.info(&follower->follower, uinfo);
 	if (err < 0) {
 		kfree(uinfo);
 		return err;
 	}
 	follower->info.type = uinfo->type;
 	follower->info.count = uinfo->count;
 	if (follower->info.count > 2  ||
 	    (follower->info.type != SNDRV_CTL_ELEM_TYPE_INTEGER &&
 	     follower->info.type != SNDRV_CTL_ELEM_TYPE_BOOLEAN)) {
 		pr_err("ALSA: vmaster: invalid follower element\n");
 		kfree(uinfo);
 		return -EINVAL;
 	}
 	follower->info.min_val = uinfo->value.integer.min;
 	follower->info.max_val = uinfo->value.integer.max;
 	kfree(uinfo);

 	return follower_update(follower);
 }

 /* initialize master volume */
 static int master_init(struct link_master *master)
 {
 	struct link_follower *follower;

 	if (master->info.count)
 		return 0; /* already initialized */

 	list_for_each_entry(follower, &master->followers, list) {
 		int err = follower_init(follower);
 		if (err < 0)
 			return err;
 		master->info = follower->info;
 		master->info.count = 1; /* always mono */
 		/* set full volume as default (= no attenuation) */
 		master->val = master->info.max_val;
 		if (master->hook)
 			master->hook(master->hook_private_data, master->val);
 		return 1;
 	}
 	return -ENOENT;
 }

 static int follower_get_val(struct link_follower *follower,
 			    struct snd_ctl_elem_value *ucontrol)
 {
 	int err, ch;

 	err = follower_init(follower);
 	if (err < 0)
 		return err;
 	for (ch = 0; ch < follower->info.count; ch++)
 		ucontrol->value.integer.value[ch] = follower->vals[ch];
 	return 0;
 }

 static int follower_put_val(struct link_follower *follower,
 			    struct snd_ctl_elem_value *ucontrol)
 {
 	int err, ch, vol;

 	err = master_init(follower->master);
 	if (err < 0)
 		return err;

 	switch (follower->info.type) {
 	case SNDRV_CTL_ELEM_TYPE_BOOLEAN:
 		for (ch = 0; ch < follower->info.count; ch++)
 			ucontrol->value.integer.value[ch] &=
 				!!follower->master->val;
 		break;
 	case SNDRV_CTL_ELEM_TYPE_INTEGER:
 		for (ch = 0; ch < follower->info.count; ch++) {
 			/* max master volume is supposed to be 0 dB */
 			vol = ucontrol->value.integer.value[ch];
 			vol += follower->master->val - follower->master->info.max_val;
 			if (vol < follower->info.min_val)
 				vol = follower->info.min_val;
 			else if (vol > follower->info.max_val)
 				vol = follower->info.max_val;
 			ucontrol->value.integer.value[ch] = vol;
 		}
 		break;
 	}
 	return follower->follower.put(&follower->follower, ucontrol);
 }

 /*
  * ctl callbacks for followers
  */
 static int follower_info(struct snd_kcontrol *kcontrol,
 			 struct snd_ctl_elem_info *uinfo)
 {
 	struct link_follower *follower = snd_kcontrol_chip(kcontrol);
 	return follower->follower.info(&follower->follower, uinfo);
 }

 static int follower_get(struct snd_kcontrol *kcontrol,
 			struct snd_ctl_elem_value *ucontrol)
 {
 	struct link_follower *follower = snd_kcontrol_chip(kcontrol);
 	return follower_get_val(follower, ucontrol);
 }

 static int follower_put(struct snd_kcontrol *kcontrol,
 			struct snd_ctl_elem_value *ucontrol)
 {
 	struct link_follower *follower = snd_kcontrol_chip(kcontrol);
 	int err, ch, changed = 0;

 	err = follower_init(follower);
 	if (err < 0)
 		return err;
 	for (ch = 0; ch < follower->info.count; ch++) {
 		if (follower->vals[ch] != ucontrol->value.integer.value[ch]) {
 			changed = 1;
 			follower->vals[ch] = ucontrol->value.integer.value[ch];
 		}
 	}
 	if (!changed)
 		return 0;
 	err = follower_put_val(follower, ucontrol);
 	if (err < 0)
 		return err;
 	return 1;
 }

 static int follower_tlv_cmd(struct snd_kcontrol *kcontrol,
 			    int op_flag, unsigned int size,
 			    unsigned int __user *tlv)
 {
 	struct link_follower *follower = snd_kcontrol_chip(kcontrol);
 	/* FIXME: this assumes that the max volume is 0 dB */
 	return follower->follower.tlv.c(&follower->follower, op_flag, size, tlv);
 }

 static void follower_free(struct snd_kcontrol *kcontrol)
 {
 	struct link_follower *follower = snd_kcontrol_chip(kcontrol);
 	if (follower->follower.private_free)
 		follower->follower.private_free(&follower->follower);
 	if (follower->master)
 		list_del(&follower->list);
 	kfree(follower);
 }

 /*
  * Add a follower control to the group with the given master control
  *
  * All followers must be the same type (returning the same information
  * via info callback).  The function doesn't check it, so it's your
  * responsibility.
  *
  * Also, some additional limitations:
  * - at most two channels
  * - logarithmic volume control (dB level), no linear volume
  * - master can only attenuate the volume, no gain
  */
 int _snd_ctl_add_follower(struct snd_kcontrol *master,
 			  struct snd_kcontrol *follower,
 			  unsigned int flags)
 {
 	struct link_master *master_link = snd_kcontrol_chip(master);
 	struct link_follower *srec;

 	srec = kzalloc(struct_size(srec, follower.vd, follower->count),
 		       GFP_KERNEL);
 	if (!srec)
 		return -ENOMEM;
 	srec->kctl = follower;
 	srec->follower = *follower;
 	memcpy(srec->follower.vd, follower->vd, follower->count * sizeof(*follower->vd));
 	srec->master = master_link;
 	srec->flags = flags;

 	/* override callbacks */
 	follower->info = follower_info;
 	follower->get = follower_get;
 	follower->put = follower_put;
 	if (follower->vd[0].access & SNDRV_CTL_ELEM_ACCESS_TLV_CALLBACK)
 		follower->tlv.c = follower_tlv_cmd;
 	follower->private_data = srec;
 	follower->private_free = follower_free;

 	list_add_tail(&srec->list, &master_link->followers);
 	return 0;
 }
 EXPORT_SYMBOL(_snd_ctl_add_follower);

 /*
  * ctl callbacks for master controls
  */
 static int master_info(struct snd_kcontrol *kcontrol,
 		      struct snd_ctl_elem_info *uinfo)
 {
 	struct link_master *master = snd_kcontrol_chip(kcontrol);
 	int ret;

 	ret = master_init(master);
 	if (ret < 0)
 		return ret;
 	uinfo->type = master->info.type;
 	uinfo->count = master->info.count;
 	uinfo->value.integer.min = master->info.min_val;
 	uinfo->value.integer.max = master->info.max_val;
 	return 0;
 }

 static int master_get(struct snd_kcontrol *kcontrol,
 		      struct snd_ctl_elem_value *ucontrol)
 {
 	struct link_master *master = snd_kcontrol_chip(kcontrol);
 	int err = master_init(master);
 	if (err < 0)
 		return err;
 	ucontrol->value.integer.value[0] = master->val;
 	return 0;
 }

 static int sync_followers(struct link_master *master, int old_val, int new_val)
 {
 	struct link_follower *follower;
 	struct snd_ctl_elem_value *uval;

 	uval = kmalloc(sizeof(*uval), GFP_KERNEL);
 	if (!uval)
 		return -ENOMEM;
 	list_for_each_entry(follower, &master->followers, list) {
 		master->val = old_val;
 		uval->id = follower->follower.id;
 		follower_get_val(follower, uval);
 		master->val = new_val;
 		follower_put_val(follower, uval);
 	}
 	kfree(uval);
 	return 0;
 }

 static int master_put(struct snd_kcontrol *kcontrol,
 		      struct snd_ctl_elem_value *ucontrol)
 {
 	struct link_master *master = snd_kcontrol_chip(kcontrol);
 	int err, new_val, old_val;
 	bool first_init;

 	err = master_init(master);
 	if (err < 0)
 		return err;
 	first_init = err;
 	old_val = master->val;
 	new_val = ucontrol->value.integer.value[0];
 	if (new_val == old_val)
 		return 0;

 	err = sync_followers(master, old_val, new_val);
 	if (err < 0)
 		return err;
 	if (master->hook && !first_init)
 		master->hook(master->hook_private_data, master->val);
 	return 1;
 }

 static void master_free(struct snd_kcontrol *kcontrol)
 {
 	struct link_master *master = snd_kcontrol_chip(kcontrol);
 	struct link_follower *follower, *n;

 	/* free all follower links and retore the original follower kctls */
 	list_for_each_entry_safe(follower, n, &master->followers, list) {
 		struct snd_kcontrol *sctl = follower->kctl;
 		struct list_head olist = sctl->list;
 		memcpy(sctl, &follower->follower, sizeof(*sctl));
 		memcpy(sctl->vd, follower->follower.vd,
 		       sctl->count * sizeof(*sctl->vd));
 		sctl->list = olist; /* keep the current linked-list */
 		kfree(follower);
 	}
 	kfree(master);
 }


 /**
  * snd_ctl_make_virtual_master - Create a virtual master control
  * @name: name string of the control element to create
  * @tlv: optional TLV int array for dB information
  *
  * Creates a virtual master control with the given name string.
  *
  * After creating a vmaster element, you can add the follower controls
  * via snd_ctl_add_follower() or snd_ctl_add_follower_uncached().
  *
  * The optional argument @tlv can be used to specify the TLV information
  * for dB scale of the master control.  It should be a single element
  * with #SNDRV_CTL_TLVT_DB_SCALE, #SNDRV_CTL_TLV_DB_MINMAX or
  * #SNDRV_CTL_TLVT_DB_MINMAX_MUTE type, and should be the max 0dB.
  *
  * Return: The created control element, or %NULL for errors (ENOMEM).
  */
 struct snd_kcontrol *snd_ctl_make_virtual_master(char *name,
 						 const unsigned int *tlv)
 {
 	struct link_master *master;
 	struct snd_kcontrol *kctl;
 	struct snd_kcontrol_new knew;

 	memset(&knew, 0, sizeof(knew));
 	knew.iface = SNDRV_CTL_ELEM_IFACE_MIXER;
 	knew.name = name;
 	knew.info = master_info;

 	master = kzalloc(sizeof(*master), GFP_KERNEL);
 	if (!master)
 		return NULL;
 	INIT_LIST_HEAD(&master->followers);

 	kctl = snd_ctl_new1(&knew, master);
 	if (!kctl) {
 		kfree(master);
 		return NULL;
 	}
 	/* override some callbacks */
 	kctl->info = master_info;
 	kctl->get = master_get;
 	kctl->put = master_put;
 	kctl->private_free = master_free;

 	/* additional (constant) TLV read */
 	if (tlv) {
 		unsigned int type = tlv[SNDRV_CTL_TLVO_TYPE];
 		if (type == SNDRV_CTL_TLVT_DB_SCALE ||
 		    type == SNDRV_CTL_TLVT_DB_MINMAX ||
 		    type == SNDRV_CTL_TLVT_DB_MINMAX_MUTE) {
 			kctl->vd[0].access |= SNDRV_CTL_ELEM_ACCESS_TLV_READ;
 			memcpy(master->tlv, tlv, sizeof(master->tlv));
 			kctl->tlv.p = master->tlv;
 		}
 	}

 	return kctl;
 }
 EXPORT_SYMBOL(snd_ctl_make_virtual_master);

 /**
  * snd_ctl_add_vmaster_hook - Add a hook to a vmaster control
  * @kcontrol: vmaster kctl element
  * @hook: the hook function
  * @private_data: the private_data pointer to be saved
  *
  * Adds the given hook to the vmaster control element so that it's called
  * at each time when the value is changed.
  *
  * Return: Zero.
  */
 int snd_ctl_add_vmaster_hook(struct snd_kcontrol *kcontrol,
 			     void (*hook)(void *private_data, int),
 			     void *private_data)
 {
 	struct link_master *master = snd_kcontrol_chip(kcontrol);
 	master->hook = hook;
 	master->hook_private_data = private_data;
 	return 0;
 }
 EXPORT_SYMBOL_GPL(snd_ctl_add_vmaster_hook);

 /**
  * snd_ctl_sync_vmaster - Sync the vmaster followers and hook
  * @kcontrol: vmaster kctl element
  * @hook_only: sync only the hook
  *
  * Forcibly call the put callback of each follower and call the hook function
  * to synchronize with the current value of the given vmaster element.
  * NOP when NULL is passed to @kcontrol.
  */
 void snd_ctl_sync_vmaster(struct snd_kcontrol *kcontrol, bool hook_only)
 {
 	struct link_master *master;
 	bool first_init = false;

 	if (!kcontrol)
 		return;
 	master = snd_kcontrol_chip(kcontrol);
 	if (!hook_only) {
 		int err = master_init(master);
 		if (err < 0)
 			return;
 		first_init = err;
 		err = sync_followers(master, master->val, master->val);
 		if (err < 0)
 			return;
 	}

 	if (master->hook && !first_init)
 		master->hook(master->hook_private_data, master->val);
 }
 EXPORT_SYMBOL_GPL(snd_ctl_sync_vmaster);

 /**
  * snd_ctl_apply_vmaster_followers - Apply function to each vmaster follower
  * @kctl: vmaster kctl element
  * @func: function to apply
  * @arg: optional function argument
  *
  * Apply the function @func to each follower kctl of the given vmaster kctl.
  * Returns 0 if successful, or a negative error code.
  */
 int snd_ctl_apply_vmaster_followers(struct snd_kcontrol *kctl,
 				    int (*func)(struct snd_kcontrol *vfollower,
 						struct snd_kcontrol *follower,
 						void *arg),
 				    void *arg)
 {
 	struct link_master *master;
 	struct link_follower *follower;
 	int err;

 	master = snd_kcontrol_chip(kctl);
 	err = master_init(master);
 	if (err < 0)
 		return err;
 	list_for_each_entry(follower, &master->followers, list) {
 		err = func(follower->kctl, &follower->follower, arg);
 		if (err < 0)
 			return err;
 	}

 	return 0;
 }
 EXPORT_SYMBOL_GPL(snd_ctl_apply_vmaster_followers);
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* Virtual master and follower controls
	*
	* Copyright (c) 2008 by Takashi Iwai <tiwai@suse.de>
	*/

	#include <linux/slab.h>
	#include <linux/export.h>
	#include <sound/core.h>
	#include <sound/control.h>
	#include <sound/tlv.h>

	/*
	* a subset of information returned via ctl info callback
	*/
	struct link_ctl_info {
	snd_ctl_elem_type_t type; /* value type */
	int count; /* item count */
	int min_val, max_val; /* min, max values */
	};

	/*
	* link master - this contains a list of follower controls that are
	* identical types, i.e. info returns the same value type and value
	* ranges, but may have different number of counts.
	*
	* The master control is so far only mono volume/switch for simplicity.
	* The same value will be applied to all followers.
	*/
	struct link_master {
	struct list_head followers;
	struct link_ctl_info info;
	int val; /* the master value */
	unsigned int tlv[4];
	void (hook)(void private_data, int);
	void *hook_private_data;
	};

	/*
	* link follower - this contains a follower control element
	*
	* It fakes the control callbacks with additional attenuation by the
	* master control. A follower may have either one or two channels.
	*/

	struct link_follower {
	struct list_head list;
	struct link_master *master;
	struct link_ctl_info info;
	int vals[2]; /* current values */
	unsigned int flags;
	struct snd_kcontrol kctl; / original kcontrol pointer */
	struct snd_kcontrol follower; /* the copy of original control entry */
	};

	static int follower_update(struct link_follower *follower)
	{
	struct snd_ctl_elem_value *uctl;
	int err, ch;

	uctl = kzalloc(sizeof(*uctl), GFP_KERNEL);
	if (!uctl)
	return -ENOMEM;
	uctl->id = follower->follower.id;
	err = follower->follower.get(&follower->follower, uctl);
	if (err < 0)
	goto error;
	for (ch = 0; ch < follower->info.count; ch++)
	follower->vals[ch] = uctl->value.integer.value[ch];
	error:
	kfree(uctl);
	return err < 0 ? err : 0;
	}

	/* get the follower ctl info and save the initial values */
	static int follower_init(struct link_follower *follower)
	{
	struct snd_ctl_elem_info *uinfo;
	int err;

	if (follower->info.count) {
	/* already initialized */
	if (follower->flags & SND_CTL_FOLLOWER_NEED_UPDATE)
	return follower_update(follower);
	return 0;
	}

	uinfo = kmalloc(sizeof(*uinfo), GFP_KERNEL);
	if (!uinfo)
	return -ENOMEM;
	uinfo->id = follower->follower.id;
	err = follower->follower.info(&follower->follower, uinfo);
	if (err < 0) {
	kfree(uinfo);
	return err;
	}
	follower->info.type = uinfo->type;
	follower->info.count = uinfo->count;
	if (follower->info.count > 2 \|\|
	(follower->info.type != SNDRV_CTL_ELEM_TYPE_INTEGER &&
	follower->info.type != SNDRV_CTL_ELEM_TYPE_BOOLEAN)) {
	pr_err("ALSA: vmaster: invalid follower element\n");
	kfree(uinfo);
	return -EINVAL;
	}
	follower->info.min_val = uinfo->value.integer.min;
	follower->info.max_val = uinfo->value.integer.max;
	kfree(uinfo);

	return follower_update(follower);
	}

	/* initialize master volume */
	static int master_init(struct link_master *master)
	{
	struct link_follower *follower;

	if (master->info.count)
	return 0; /* already initialized */

	list_for_each_entry(follower, &master->followers, list) {
	int err = follower_init(follower);
	if (err < 0)
	return err;
	master->info = follower->info;
	master->info.count = 1; /* always mono */
	/* set full volume as default (= no attenuation) */
	master->val = master->info.max_val;
	if (master->hook)
	master->hook(master->hook_private_data, master->val);
	return 1;
	}
	return -ENOENT;
	}

	static int follower_get_val(struct link_follower *follower,
	struct snd_ctl_elem_value *ucontrol)
	{
	int err, ch;

	err = follower_init(follower);
	if (err < 0)
	return err;
	for (ch = 0; ch < follower->info.count; ch++)
	ucontrol->value.integer.value[ch] = follower->vals[ch];
	return 0;
	}

	static int follower_put_val(struct link_follower *follower,
	struct snd_ctl_elem_value *ucontrol)
	{
	int err, ch, vol;

	err = master_init(follower->master);
	if (err < 0)
	return err;

	switch (follower->info.type) {
	case SNDRV_CTL_ELEM_TYPE_BOOLEAN:
	for (ch = 0; ch < follower->info.count; ch++)
	ucontrol->value.integer.value[ch] &=
	!!follower->master->val;
	break;
	case SNDRV_CTL_ELEM_TYPE_INTEGER:
	for (ch = 0; ch < follower->info.count; ch++) {
	/* max master volume is supposed to be 0 dB */
	vol = ucontrol->value.integer.value[ch];
	vol += follower->master->val - follower->master->info.max_val;
	if (vol < follower->info.min_val)
	vol = follower->info.min_val;
	else if (vol > follower->info.max_val)
	vol = follower->info.max_val;
	ucontrol->value.integer.value[ch] = vol;
	}
	break;
	}
	return follower->follower.put(&follower->follower, ucontrol);
	}

	/*
	* ctl callbacks for followers
	*/
	static int follower_info(struct snd_kcontrol *kcontrol,
	struct snd_ctl_elem_info *uinfo)
	{
	struct link_follower *follower = snd_kcontrol_chip(kcontrol);
	return follower->follower.info(&follower->follower, uinfo);
	}

	static int follower_get(struct snd_kcontrol *kcontrol,
	struct snd_ctl_elem_value *ucontrol)
	{
	struct link_follower *follower = snd_kcontrol_chip(kcontrol);
	return follower_get_val(follower, ucontrol);
	}

	static int follower_put(struct snd_kcontrol *kcontrol,
	struct snd_ctl_elem_value *ucontrol)
	{
	struct link_follower *follower = snd_kcontrol_chip(kcontrol);
	int err, ch, changed = 0;

	err = follower_init(follower);
	if (err < 0)
	return err;
	for (ch = 0; ch < follower->info.count; ch++) {
	if (follower->vals[ch] != ucontrol->value.integer.value[ch]) {
	changed = 1;
	follower->vals[ch] = ucontrol->value.integer.value[ch];
	}
	}
	if (!changed)
	return 0;
	err = follower_put_val(follower, ucontrol);
	if (err < 0)
	return err;
	return 1;
	}

	static int follower_tlv_cmd(struct snd_kcontrol *kcontrol,
	int op_flag, unsigned int size,
	unsigned int __user *tlv)
	{
	struct link_follower *follower = snd_kcontrol_chip(kcontrol);
	/* FIXME: this assumes that the max volume is 0 dB */
	return follower->follower.tlv.c(&follower->follower, op_flag, size, tlv);
	}

	static void follower_free(struct snd_kcontrol *kcontrol)
	{
	struct link_follower *follower = snd_kcontrol_chip(kcontrol);
	if (follower->follower.private_free)
	follower->follower.private_free(&follower->follower);
	if (follower->master)
	list_del(&follower->list);
	kfree(follower);
	}

	/*
	* Add a follower control to the group with the given master control
	*
	* All followers must be the same type (returning the same information
	* via info callback). The function doesn't check it, so it's your
	* responsibility.
	*
	* Also, some additional limitations:
	* - at most two channels
	* - logarithmic volume control (dB level), no linear volume
	* - master can only attenuate the volume, no gain
	*/
	int _snd_ctl_add_follower(struct snd_kcontrol *master,
	struct snd_kcontrol *follower,
	unsigned int flags)
	{
	struct link_master *master_link = snd_kcontrol_chip(master);
	struct link_follower *srec;

	srec = kzalloc(struct_size(srec, follower.vd, follower->count),
	GFP_KERNEL);
	if (!srec)
	return -ENOMEM;
	srec->kctl = follower;
	srec->follower = *follower;
	memcpy(srec->follower.vd, follower->vd, follower->count * sizeof(*follower->vd));
	srec->master = master_link;
	srec->flags = flags;

	/* override callbacks */
	follower->info = follower_info;
	follower->get = follower_get;
	follower->put = follower_put;
	if (follower->vd[0].access & SNDRV_CTL_ELEM_ACCESS_TLV_CALLBACK)
	follower->tlv.c = follower_tlv_cmd;
	follower->private_data = srec;
	follower->private_free = follower_free;

	list_add_tail(&srec->list, &master_link->followers);
	return 0;
	}
	EXPORT_SYMBOL(_snd_ctl_add_follower);

	/*
	* ctl callbacks for master controls
	*/
	static int master_info(struct snd_kcontrol *kcontrol,
	struct snd_ctl_elem_info *uinfo)
	{
	struct link_master *master = snd_kcontrol_chip(kcontrol);
	int ret;

	ret = master_init(master);
	if (ret < 0)
	return ret;
	uinfo->type = master->info.type;
	uinfo->count = master->info.count;
	uinfo->value.integer.min = master->info.min_val;
	uinfo->value.integer.max = master->info.max_val;
	return 0;
	}

	static int master_get(struct snd_kcontrol *kcontrol,
	struct snd_ctl_elem_value *ucontrol)
	{
	struct link_master *master = snd_kcontrol_chip(kcontrol);
	int err = master_init(master);
	if (err < 0)
	return err;
	ucontrol->value.integer.value[0] = master->val;
	return 0;
	}

	static int sync_followers(struct link_master *master, int old_val, int new_val)
	{
	struct link_follower *follower;
	struct snd_ctl_elem_value *uval;

	uval = kmalloc(sizeof(*uval), GFP_KERNEL);
	if (!uval)
	return -ENOMEM;
	list_for_each_entry(follower, &master->followers, list) {
	master->val = old_val;
	uval->id = follower->follower.id;
	follower_get_val(follower, uval);
	master->val = new_val;
	follower_put_val(follower, uval);
	}
	kfree(uval);
	return 0;
	}

	static int master_put(struct snd_kcontrol *kcontrol,
	struct snd_ctl_elem_value *ucontrol)
	{
	struct link_master *master = snd_kcontrol_chip(kcontrol);
	int err, new_val, old_val;
	bool first_init;

	err = master_init(master);
	if (err < 0)
	return err;
	first_init = err;
	old_val = master->val;
	new_val = ucontrol->value.integer.value[0];
	if (new_val == old_val)
	return 0;

	err = sync_followers(master, old_val, new_val);
	if (err < 0)
	return err;
	if (master->hook && !first_init)
	master->hook(master->hook_private_data, master->val);
	return 1;
	}

	static void master_free(struct snd_kcontrol *kcontrol)
	{
	struct link_master *master = snd_kcontrol_chip(kcontrol);
	struct link_follower follower, n;

	/* free all follower links and retore the original follower kctls */
	list_for_each_entry_safe(follower, n, &master->followers, list) {
	struct snd_kcontrol *sctl = follower->kctl;
	struct list_head olist = sctl->list;
	memcpy(sctl, &follower->follower, sizeof(*sctl));
	memcpy(sctl->vd, follower->follower.vd,
	sctl->count * sizeof(*sctl->vd));
	sctl->list = olist; /* keep the current linked-list */
	kfree(follower);
	}
	kfree(master);
	}


	/**
	* snd_ctl_make_virtual_master - Create a virtual master control
	* @name: name string of the control element to create
	* @tlv: optional TLV int array for dB information
	*
	* Creates a virtual master control with the given name string.
	*
	* After creating a vmaster element, you can add the follower controls
	* via snd_ctl_add_follower() or snd_ctl_add_follower_uncached().
	*
	* The optional argument @tlv can be used to specify the TLV information
	* for dB scale of the master control. It should be a single element
	* with #SNDRV_CTL_TLVT_DB_SCALE, #SNDRV_CTL_TLV_DB_MINMAX or
	* #SNDRV_CTL_TLVT_DB_MINMAX_MUTE type, and should be the max 0dB.
	*
	* Return: The created control element, or %NULL for errors (ENOMEM).
	*/
	struct snd_kcontrol snd_ctl_make_virtual_master(char name,
	const unsigned int *tlv)
	{
	struct link_master *master;
	struct snd_kcontrol *kctl;
	struct snd_kcontrol_new knew;

	memset(&knew, 0, sizeof(knew));
	knew.iface = SNDRV_CTL_ELEM_IFACE_MIXER;
	knew.name = name;
	knew.info = master_info;

	master = kzalloc(sizeof(*master), GFP_KERNEL);
	if (!master)
	return NULL;
	INIT_LIST_HEAD(&master->followers);

	kctl = snd_ctl_new1(&knew, master);
	if (!kctl) {
	kfree(master);
	return NULL;
	}
	/* override some callbacks */
	kctl->info = master_info;
	kctl->get = master_get;
	kctl->put = master_put;
	kctl->private_free = master_free;

	/* additional (constant) TLV read */
	if (tlv) {
	unsigned int type = tlv[SNDRV_CTL_TLVO_TYPE];
	if (type == SNDRV_CTL_TLVT_DB_SCALE \|\|
	type == SNDRV_CTL_TLVT_DB_MINMAX \|\|
	type == SNDRV_CTL_TLVT_DB_MINMAX_MUTE) {
	kctl->vd[0].access \|= SNDRV_CTL_ELEM_ACCESS_TLV_READ;
	memcpy(master->tlv, tlv, sizeof(master->tlv));
	kctl->tlv.p = master->tlv;
	}
	}

	return kctl;
	}
	EXPORT_SYMBOL(snd_ctl_make_virtual_master);

	/**
	* snd_ctl_add_vmaster_hook - Add a hook to a vmaster control
	* @kcontrol: vmaster kctl element
	* @hook: the hook function
	* @private_data: the private_data pointer to be saved
	*
	* Adds the given hook to the vmaster control element so that it's called
	* at each time when the value is changed.
	*
	* Return: Zero.
	*/
	int snd_ctl_add_vmaster_hook(struct snd_kcontrol *kcontrol,
	void (hook)(void private_data, int),
	void *private_data)
	{
	struct link_master *master = snd_kcontrol_chip(kcontrol);
	master->hook = hook;
	master->hook_private_data = private_data;
	return 0;
	}
	EXPORT_SYMBOL_GPL(snd_ctl_add_vmaster_hook);

	/**
	* snd_ctl_sync_vmaster - Sync the vmaster followers and hook
	* @kcontrol: vmaster kctl element
	* @hook_only: sync only the hook
	*
	* Forcibly call the put callback of each follower and call the hook function
	* to synchronize with the current value of the given vmaster element.
	* NOP when NULL is passed to @kcontrol.
	*/
	void snd_ctl_sync_vmaster(struct snd_kcontrol *kcontrol, bool hook_only)
	{
	struct link_master *master;
	bool first_init = false;

	if (!kcontrol)
	return;
	master = snd_kcontrol_chip(kcontrol);
	if (!hook_only) {
	int err = master_init(master);
	if (err < 0)
	return;
	first_init = err;
	err = sync_followers(master, master->val, master->val);
	if (err < 0)
	return;
	}

	if (master->hook && !first_init)
	master->hook(master->hook_private_data, master->val);
	}
	EXPORT_SYMBOL_GPL(snd_ctl_sync_vmaster);

	/**
	* snd_ctl_apply_vmaster_followers - Apply function to each vmaster follower
	* @kctl: vmaster kctl element
	* @func: function to apply
	* @arg: optional function argument
	*
	* Apply the function @func to each follower kctl of the given vmaster kctl.
	* Returns 0 if successful, or a negative error code.
	*/
	int snd_ctl_apply_vmaster_followers(struct snd_kcontrol *kctl,
	int (func)(struct snd_kcontrol vfollower,
	struct snd_kcontrol *follower,
	void *arg),
	void *arg)
	{
	struct link_master *master;
	struct link_follower *follower;
	int err;

	master = snd_kcontrol_chip(kctl);
	err = master_init(master);
	if (err < 0)
	return err;
	list_for_each_entry(follower, &master->followers, list) {
	err = func(follower->kctl, &follower->follower, arg);
	if (err < 0)
	return err;
	}

	return 0;
	}
	EXPORT_SYMBOL_GPL(snd_ctl_apply_vmaster_followers);