IN operator is not working with query in VB.Net

Question

Hi, this is my stored procedure - 
-- --------------------------------------------------------------------------------
-- Routine DDL
-- Note: comments before and after the routine body will not be stored by the server
-- --------------------------------------------------------------------------------
drop procedure if exists SP_Login;


DELIMITER $$


CREATE DEFINER=`root`@`localhost` PROCEDURE `SP_Login`(_action varchar(10),
 _uname varchar(500))
BEGIN
if _action = 'SelectU' then
SELECT Name as CompanyName, Uname as UserName, Pwd,
Mobile as MobileNumber, limax as NumberofVehicles, Address,
RID as UserId, parent_user, child_user, ProfileRights, AllocationRights,
GeneralRights from Regis
WHERE UName IN (_uname) ;
end if;


END

and this is my VB.Net code - 

 dtUserDetails = DBClass.GetDataTableForLogin("SelectU", Children, "")
            grdUserProfile.DataSource = dtUserDetails

Public Function GetDataTableForLogin(ByVal action As String, ByVal uname As String) As DataTable


        Dim dtdatatable As New DataTable
        Dim conn As OdbcConnection = New OdbcConnection(ConfigurationManager.ConnectionStrings("DBConnection").ToString)
        Dim cmd As OdbcCommand = conn.CreateCommand
        cmd.CommandText = "{call SP_Login(?,?)}"
        cmd.CommandType = CommandType.StoredProcedure
        cmd.Parameters.AddWithValue("_action", action)
        cmd.Parameters.AddWithValue("_uname", uname))
        conn.Open()
        Dim da As New OdbcDataAdapter(cmd)
        da.Fill(dtdatatable)
        da.Dispose()
        conn.Close()
        Return dtdatatable

when i am running my code uname value i am getting,but after that in datatable it is coming blank.

tell me is there any problem with my code?