1 files changed, 45 insertions, 1 deletions

diff --git a/sound/core/vmaster.c b/sound/core/vmaster.c
index 130cfe677d60..14a286a7bf2b 100644
--- a/sound/core/vmaster.c
+++ b/sound/core/vmaster.c
@@ -37,6 +37,8 @@ struct link_master {
         struct link_ctl_info info;
         int val;                /* the master value */
         unsigned int tlv[4];
+        void (*hook)(void *private_data, int);
+        void *hook_private_data;
 };
 
 /*
@@ -126,7 +128,9 @@ static int master_init(struct link_master *master)
                 master->info.count = 1; /* always mono */
                 /* set full volume as default (= no attenuation) */
                 master->val = master->info.max_val;
-                return 0;
+                if (master->hook)
+                        master->hook(master->hook_private_data, master->val);
+                return 1;
         }
         return -ENOENT;
 }
@@ -329,6 +333,8 @@ static int master_put(struct snd_kcontrol *kcontrol,
                 slave_put_val(slave, uval);
         }
         kfree(uval);
+        if (master->hook && !err)
+                master->hook(master->hook_private_data, master->val);
         return 1;
 }
 
@@ -408,3 +414,41 @@ struct snd_kcontrol *snd_ctl_make_virtual_master(char *name,
         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);