Login Controller

<?php
defined('BASEPATH') OR exit('No direct script access allowed');
class Login extends CI_Controller {

    function __construct() {
        parent::__construct();
        $this->load->model('login_model');
    }
    public function index() {
        //check if i can pass some data to view
        $data['title_header'] = 'Login title';
        $this->load->view('foundation/header', $data);

        //security inputs in controller, if some data are sents
        $this->check_login();

        //loading login page
        $this->load->view("login_view");
        $this->load->view('foundation/footer');
    }
    private function check_login() {
        //check if is not empty
        if (!$this->input->post('username') && !$this->input->post('password')) {
            return;
        }
        //if i have some value i begin the test...
        $this->load->library('form_validation');
        $this->form_validation->set_rules('username', 'Name', 'required|max_length[20]');
        $this->form_validation->set_rules('password', 'Password', 'required|max_length[20]');
        //
        if ($this->form_validation->run()) {
            //if everything is ok, let's check in db
            $params = array(
                'username' => $this->input->post('username'),
                'password' => $this->input->post('password'),
                /* and username and password is secure by form validation? */
            );

            $this->login_model->check_login_database($params);
        } else {
            //how i know what is wrong?name or password?i'm confuse
            $this->session->set_flashdata('login', array('class' => 'alert alert-danger', 'message' => 'Something is wrong'));
        }
    }
}