Bluetooth: VCP: Allow for multiple vol_ctrl cb registers

include/zephyr/bluetooth/audio/vcp.h

@@ -353,17 +353,33 @@ struct bt_vcp_vol_ctlr_cb {
 
 	/* Audio Input Control Service callbacks */
 	struct bt_aics_cb             aics_cb;
+
+	/** Internally used field for list handling */
+	sys_snode_t _node;
 };
 
 /**
  * @brief Registers the callbacks used by the Volume Controller.
  *
  * @param cb   The callback structure.
  *
- * @return 0 if success, errno on failure.
+ * @retval 0 on success
+ * @retval -EINVAL if @p cb is NULL
+ * @retval -EALREADY if @p cb was already registered
  */
 int bt_vcp_vol_ctlr_cb_register(struct bt_vcp_vol_ctlr_cb *cb);
 
+/**
+ * @brief Unregisters the callbacks used by the Volume Controller.
+ *
+ * @param cb   The callback structure.
+ *
+ * @retval 0 on success
+ * @retval -EINVAL if @p cb is NULL
+ * @retval -EALREADY if @p cb was not registered
+ */
+int bt_vcp_vol_ctlr_cb_unregister(struct bt_vcp_vol_ctlr_cb *cb);
+
 /**
  * @brief Discover Volume Control Service and included services.
  *

subsys/bluetooth/audio/shell/vcp_vol_ctlr.c

@@ -326,16 +326,21 @@ static struct bt_vcp_vol_ctlr_cb vcp_cbs = {
 static int cmd_vcp_vol_ctlr_discover(const struct shell *sh, size_t argc,
 				   char **argv)
 {
+	static bool cb_registered;
 	int result;
 
 	if (!ctx_shell) {
 		ctx_shell = sh;
 	}
 
-	result = bt_vcp_vol_ctlr_cb_register(&vcp_cbs);
-	if (result != 0) {
-		shell_print(sh, "CB register failed: %d", result);
-		return result;
+	if (!cb_registered) {
+		result = bt_vcp_vol_ctlr_cb_register(&vcp_cbs);
+		if (result != 0) {
+			shell_print(sh, "CB register failed: %d", result);
+			return result;
+		}
+
+		cb_registered = true;
 	}
 
 	if (default_conn == NULL) {