sound/core/vmaster.c - kernel/msm-4.19 - Gitiles

 /*
  * Virtual master and slave controls
  *
  *  Copyright (c) 2008 by Takashi Iwai <tiwai@suse.de>
  *
  *  This program is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU General Public License as
  *  published by the Free Software Foundation, version 2.
  *
  */

 #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 slave 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 slaves.
  */
 struct link_master {
 	struct list_head slaves;
 	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 slave - this contains a slave control element
  *
  * It fakes the control callbacsk with additional attenuation by the
  * master control.  A slave may have either one or two channels.
  */

 struct link_slave {
 	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 slave; /* the copy of original control entry */
 };

 static int slave_update(struct link_slave *slave)
 {
 	struct snd_ctl_elem_value *uctl;
 	int err, ch;

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

 /* get the slave ctl info and save the initial values */
 static int slave_init(struct link_slave *slave)
 {
 	struct snd_ctl_elem_info *uinfo;
 	int err;

 	if (slave->info.count) {
 		/* already initialized */
 		if (slave->flags & SND_CTL_SLAVE_NEED_UPDATE)
 			return slave_update(slave);
 		return 0;
 	}

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

 	return slave_update(slave);
 }

 /* initialize master volume */
 static int master_init(struct link_master *master)
 {
 	struct link_slave *slave;

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

 	list_for_each_entry(slave, &master->slaves, list) {
 		int err = slave_init(slave);
 		if (err < 0)
 			return err;
 		master->info = slave->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 slave_get_val(struct link_slave *slave,
 			 struct snd_ctl_elem_value *ucontrol)
 {
 	int err, ch;

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

 static int slave_put_val(struct link_slave *slave,
 			 struct snd_ctl_elem_value *ucontrol)
 {
 	int err, ch, vol;

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

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

 /*
  * ctl callbacks for slaves
  */
 static int slave_info(struct snd_kcontrol *kcontrol,
 		      struct snd_ctl_elem_info *uinfo)
 {
 	struct link_slave *slave = snd_kcontrol_chip(kcontrol);
 	return slave->slave.info(&slave->slave, uinfo);
 }

 static int slave_get(struct snd_kcontrol *kcontrol,
 		     struct snd_ctl_elem_value *ucontrol)
 {
 	struct link_slave *slave = snd_kcontrol_chip(kcontrol);
 	return slave_get_val(slave, ucontrol);
 }

 static int slave_put(struct snd_kcontrol *kcontrol,
 		     struct snd_ctl_elem_value *ucontrol)
 {
 	struct link_slave *slave = snd_kcontrol_chip(kcontrol);
 	int err, ch, changed = 0;

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

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

 static void slave_free(struct snd_kcontrol *kcontrol)
 {
 	struct link_slave *slave = snd_kcontrol_chip(kcontrol);
 	if (slave->slave.private_free)
 		slave->slave.private_free(&slave->slave);
 	if (slave->master)
 		list_del(&slave->list);
 	kfree(slave);
 }

 /*
  * Add a slave control to the group with the given master control
  *
  * All slaves 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_slave(struct snd_kcontrol *master, struct snd_kcontrol *slave,
 		       unsigned int flags)
 {
 	struct link_master *master_link = snd_kcontrol_chip(master);
 	struct link_slave *srec;

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

 	/* override callbacks */
 	slave->info = slave_info;
 	slave->get = slave_get;
 	slave->put = slave_put;
 	if (slave->vd[0].access & SNDRV_CTL_ELEM_ACCESS_TLV_CALLBACK)
 		slave->tlv.c = slave_tlv_cmd;
 	slave->private_data = srec;
 	slave->private_free = slave_free;

 	list_add_tail(&srec->list, &master_link->slaves);
 	return 0;
 }
 EXPORT_SYMBOL(_snd_ctl_add_slave);

 /*
  * 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 master_put(struct snd_kcontrol *kcontrol,
 		      struct snd_ctl_elem_value *ucontrol)
 {
 	struct link_master *master = snd_kcontrol_chip(kcontrol);
 	struct link_slave *slave;
 	struct snd_ctl_elem_value *uval;
 	int err, old_val;

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

 	uval = kmalloc(sizeof(*uval), GFP_KERNEL);
 	if (!uval)
 		return -ENOMEM;
 	list_for_each_entry(slave, &master->slaves, list) {
 		master->val = old_val;
 		uval->id = slave->slave.id;
 		slave_get_val(slave, uval);
 		master->val = ucontrol->value.integer.value[0];
 		slave_put_val(slave, uval);
 	}
 	kfree(uval);
 	if (master->hook && !err)
 		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_slave *slave, *n;

 	/* free all slave links and retore the original slave kctls */
 	list_for_each_entry_safe(slave, n, &master->slaves, list) {
 		struct snd_kcontrol *sctl = slave->kctl;
 		struct list_head olist = sctl->list;
 		memcpy(sctl, &slave->slave, sizeof(*sctl));
 		memcpy(sctl->vd, slave->slave.vd,
 		       sctl->count * sizeof(*sctl->vd));
 		sctl->list = olist; /* keep the current linked-list */
 		kfree(slave);
 	}
 	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 matster control with the given name string.
  * Returns the created control element, or NULL for errors (ENOMEM).
  *
  * After creating a vmaster element, you can add the slave controls
  * via snd_ctl_add_slave() or snd_ctl_add_slave_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.
  */
 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->slaves);

 	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 &&
 	    (tlv[0] == SNDRV_CTL_TLVT_DB_SCALE ||
 	     tlv[0] == SNDRV_CTL_TLVT_DB_MINMAX ||
 	     tlv[0] == 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
  *
  * Adds the given hook to the vmaster control element so that it's called
  * at each time when the value is changed.
  */
 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_hook - Sync the vmaster hook
  * @kcontrol: vmaster kctl element
  *
  * Call the hook function to synchronize with the current value of the given
  * vmaster element.  NOP when NULL is passed to @kcontrol or the hook doesn't
  * exist.
  */
 void snd_ctl_sync_vmaster_hook(struct snd_kcontrol *kcontrol)
 {
 	struct link_master *master;
 	if (!kcontrol)
 		return;
 	master = snd_kcontrol_chip(kcontrol);
 	if (master->hook)
 		master->hook(master->hook_private_data, master->val);
 }
 EXPORT_SYMBOL_GPL(snd_ctl_sync_vmaster_hook);
	/*
	* Virtual master and slave controls
	*
	* Copyright (c) 2008 by Takashi Iwai <tiwai@suse.de>
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License as
	* published by the Free Software Foundation, version 2.
	*
	*/

	#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 slave 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 slaves.
	*/
	struct link_master {
	struct list_head slaves;
	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 slave - this contains a slave control element
	*
	* It fakes the control callbacsk with additional attenuation by the
	* master control. A slave may have either one or two channels.
	*/

	struct link_slave {
	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 slave; /* the copy of original control entry */
	};

	static int slave_update(struct link_slave *slave)
	{
	struct snd_ctl_elem_value *uctl;
	int err, ch;

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

	/* get the slave ctl info and save the initial values */
	static int slave_init(struct link_slave *slave)
	{
	struct snd_ctl_elem_info *uinfo;
	int err;

	if (slave->info.count) {
	/* already initialized */
	if (slave->flags & SND_CTL_SLAVE_NEED_UPDATE)
	return slave_update(slave);
	return 0;
	}

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

	return slave_update(slave);
	}

	/* initialize master volume */
	static int master_init(struct link_master *master)
	{
	struct link_slave *slave;

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

	list_for_each_entry(slave, &master->slaves, list) {
	int err = slave_init(slave);
	if (err < 0)
	return err;
	master->info = slave->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 slave_get_val(struct link_slave *slave,
	struct snd_ctl_elem_value *ucontrol)
	{
	int err, ch;

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

	static int slave_put_val(struct link_slave *slave,
	struct snd_ctl_elem_value *ucontrol)
	{
	int err, ch, vol;

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

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

	/*
	* ctl callbacks for slaves
	*/
	static int slave_info(struct snd_kcontrol *kcontrol,
	struct snd_ctl_elem_info *uinfo)
	{
	struct link_slave *slave = snd_kcontrol_chip(kcontrol);
	return slave->slave.info(&slave->slave, uinfo);
	}

	static int slave_get(struct snd_kcontrol *kcontrol,
	struct snd_ctl_elem_value *ucontrol)
	{
	struct link_slave *slave = snd_kcontrol_chip(kcontrol);
	return slave_get_val(slave, ucontrol);
	}

	static int slave_put(struct snd_kcontrol *kcontrol,
	struct snd_ctl_elem_value *ucontrol)
	{
	struct link_slave *slave = snd_kcontrol_chip(kcontrol);
	int err, ch, changed = 0;

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

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

	static void slave_free(struct snd_kcontrol *kcontrol)
	{
	struct link_slave *slave = snd_kcontrol_chip(kcontrol);
	if (slave->slave.private_free)
	slave->slave.private_free(&slave->slave);
	if (slave->master)
	list_del(&slave->list);
	kfree(slave);
	}

	/*
	* Add a slave control to the group with the given master control
	*
	* All slaves 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_slave(struct snd_kcontrol master, struct snd_kcontrol slave,
	unsigned int flags)
	{
	struct link_master *master_link = snd_kcontrol_chip(master);
	struct link_slave *srec;

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

	/* override callbacks */
	slave->info = slave_info;
	slave->get = slave_get;
	slave->put = slave_put;
	if (slave->vd[0].access & SNDRV_CTL_ELEM_ACCESS_TLV_CALLBACK)
	slave->tlv.c = slave_tlv_cmd;
	slave->private_data = srec;
	slave->private_free = slave_free;

	list_add_tail(&srec->list, &master_link->slaves);
	return 0;
	}
	EXPORT_SYMBOL(_snd_ctl_add_slave);

	/*
	* 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 master_put(struct snd_kcontrol *kcontrol,
	struct snd_ctl_elem_value *ucontrol)
	{
	struct link_master *master = snd_kcontrol_chip(kcontrol);
	struct link_slave *slave;
	struct snd_ctl_elem_value *uval;
	int err, old_val;

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

	uval = kmalloc(sizeof(*uval), GFP_KERNEL);
	if (!uval)
	return -ENOMEM;
	list_for_each_entry(slave, &master->slaves, list) {
	master->val = old_val;
	uval->id = slave->slave.id;
	slave_get_val(slave, uval);
	master->val = ucontrol->value.integer.value[0];
	slave_put_val(slave, uval);
	}
	kfree(uval);
	if (master->hook && !err)
	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_slave slave, n;

	/* free all slave links and retore the original slave kctls */
	list_for_each_entry_safe(slave, n, &master->slaves, list) {
	struct snd_kcontrol *sctl = slave->kctl;
	struct list_head olist = sctl->list;
	memcpy(sctl, &slave->slave, sizeof(*sctl));
	memcpy(sctl->vd, slave->slave.vd,
	sctl->count * sizeof(*sctl->vd));
	sctl->list = olist; /* keep the current linked-list */
	kfree(slave);
	}
	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 matster control with the given name string.
	* Returns the created control element, or NULL for errors (ENOMEM).
	*
	* After creating a vmaster element, you can add the slave controls
	* via snd_ctl_add_slave() or snd_ctl_add_slave_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.
	*/
	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->slaves);

	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 &&
	(tlv[0] == SNDRV_CTL_TLVT_DB_SCALE \|\|
	tlv[0] == SNDRV_CTL_TLVT_DB_MINMAX \|\|
	tlv[0] == 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
	*
	* Adds the given hook to the vmaster control element so that it's called
	* at each time when the value is changed.
	*/
	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_hook - Sync the vmaster hook
	* @kcontrol: vmaster kctl element
	*
	* Call the hook function to synchronize with the current value of the given
	* vmaster element. NOP when NULL is passed to @kcontrol or the hook doesn't
	* exist.
	*/
	void snd_ctl_sync_vmaster_hook(struct snd_kcontrol *kcontrol)
	{
	struct link_master *master;
	if (!kcontrol)
	return;
	master = snd_kcontrol_chip(kcontrol);
	if (master->hook)
	master->hook(master->hook_private_data, master->val);
	}
	EXPORT_SYMBOL_GPL(snd_ctl_sync_vmaster_hook);