3 files changed, 97 insertions, 21 deletions

diff --git a/Documentation/sound/alsa/DocBook/alsa-driver-api.tmpl b/Documentation/sound/alsa/DocBook/alsa-driver-api.tmpl
index 37b006c..90f163c 100644
--- a/Documentation/sound/alsa/DocBook/alsa-driver-api.tmpl
+++ b/Documentation/sound/alsa/DocBook/alsa-driver-api.tmpl
@@ -71,6 +71,10 @@
 !Esound/pci/ac97/ac97_codec.c
 !Esound/pci/ac97/ac97_pcm.c
      </sect1>
+     <sect1><title>Virtual Master Control API</title>
+!Esound/core/vmaster.c
+!Iinclude/sound/control.h
+     </sect1>
   </chapter>
   <chapter><title>MIDI API</title>
      <sect1><title>Raw MIDI API</title>
diff --git a/include/sound/control.h b/include/sound/control.h
index 4721b4b..ef96f07 100644
--- a/include/sound/control.h
+++ b/include/sound/control.h
@@ -171,6 +171,54 @@ int snd_ctl_boolean_stereo_info(struct snd_kcontrol *kcontrol,
  */
 struct snd_kcontrol *snd_ctl_make_virtual_master(char *name,
 						 const unsigned int *tlv);
-int snd_ctl_add_slave(struct snd_kcontrol *master, struct snd_kcontrol *slave);
-		      
+int _snd_ctl_add_slave(struct snd_kcontrol *master, struct snd_kcontrol *slave,
+		       unsigned int flags);
+/* optional flags for slave */
+#define SND_CTL_SLAVE_NEED_UPDATE	(1 << 0)
+
+/**
+ * snd_ctl_add_slave - Add a virtual slave control
+ * @master: vmaster element
+ * @slave: slave element to add
+ *
+ * Add a virtual slave control to the given master element created via
+ * snd_ctl_create_virtual_master() beforehand.
+ * Returns zero if successful or a negative error code.
+ *
+ * All slaves must be the same type (returning the same information
+ * via info callback).  The fucntion doesn't check it, so it's your
+ * responsibility.
+ *
+ * Also, some additional limitations:
+ * at most two channels,
+ * logarithmic volume control (dB level) thus no linear volume,
+ * master can only attenuate the volume without gain
+ */
+static inline int
+snd_ctl_add_slave(struct snd_kcontrol *master, struct snd_kcontrol *slave)
+{
+	return _snd_ctl_add_slave(master, slave, 0);
+}
+
+/**
+ * snd_ctl_add_slave_uncached - Add a virtual slave control
+ * @master: vmaster element
+ * @slave: slave element to add
+ *
+ * Add a virtual slave control to the given master.
+ * Unlike snd_ctl_add_slave(), the element added via this function
+ * is supposed to have volatile values, and get callback is called
+ * at each time quried from the master.
+ *
+ * When the control peeks the hardware values directly and the value
+ * can be changed by other means than the put callback of the element,
+ * this function should be used to keep the value always up-to-date.
+ */
+static inline int
+snd_ctl_add_slave_uncached(struct snd_kcontrol *master,
+			   struct snd_kcontrol *slave)
+{
+	return _snd_ctl_add_slave(master, slave, SND_CTL_SLAVE_NEED_UPDATE);
+}
+
 #endif	/* __SOUND_CONTROL_H */
diff --git a/sound/core/vmaster.c b/sound/core/vmaster.c
index 4cc57f9..257624b 100644
--- a/sound/core/vmaster.c
+++ b/sound/core/vmaster.c
@@ -50,18 +50,38 @@ struct link_slave {
 	struct link_master *master;
 	struct link_ctl_info info;
 	int vals[2];		/* current values */
+	unsigned int flags;
 	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;
-	struct snd_ctl_elem_value *uctl;
-	int err, ch;
+	int err;
 
-	if (slave->info.count)
-		return 0; /* already initialized */
+	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)
@@ -85,15 +105,7 @@ static int slave_init(struct link_slave *slave)
 	slave->info.max_val = uinfo->value.integer.max;
 	kfree(uinfo);
 
-	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;
+	return slave_update(slave);
 }
 
 /* initialize master volume */
@@ -229,7 +241,8 @@ static void slave_free(struct snd_kcontrol *kcontrol)
  * - 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)
+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;
@@ -241,6 +254,7 @@ int snd_ctl_add_slave(struct snd_kcontrol *master, struct snd_kcontrol *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;
@@ -254,8 +268,7 @@ int snd_ctl_add_slave(struct snd_kcontrol *master, struct snd_kcontrol *slave)
 	list_add_tail(&srec->list, &master_link->slaves);
 	return 0;
 }
-
-EXPORT_SYMBOL(snd_ctl_add_slave);
+EXPORT_SYMBOL(_snd_ctl_add_slave);
 
 /*
  * ctl callbacks for master controls
@@ -327,8 +340,20 @@ static void master_free(struct snd_kcontrol *kcontrol)
 }
 
 
-/*
- * Create a virtual master control with the given name
+/**
+ * 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 type, and should be the max 0dB.
  */
 struct snd_kcontrol *snd_ctl_make_virtual_master(char *name,
 						 const unsigned int *tlv)
@@ -367,5 +392,4 @@ struct snd_kcontrol *snd_ctl_make_virtual_master(char *name,
 
 	return kctl;
 }
-
 EXPORT_SYMBOL(snd_ctl_make_virtual_master);