Pls try the following setting if you want to use the default PdoDataSource:

        return array(
            "dataSources"=>array(
                "reports"=>array(
                    "connectionString"=>"mysql:host=localhost;port=3308;dbname=my_db",
                    "username"=>"root",
                    "password"=>"xyz",
                    "charset"=>"utf8",                  
                ),
            ),
        );  

or the following one with MySQLDataSource:

        return array(
            "dataSources"=>array(
                "reports"=>array(
                    "host"=>"localhost:3308",
                    "dbname" => "my_db",
                    "username"=>"root",
                    "password"=>"xyz",
                    "charset"=>"utf8",
                    "class" => "\koolreport\datasources\MySQLDataSource",
                ),
            ),
        );  

If there's any error message pls let us know. Rgds,