Upload File With CI and Ajax

==============================================================
 config for upload (../config/config.php)
==============================================================
<?php
    $config['upload_path'] = 'upload/';
    $config['upload_tipe'] = 'gif|jpg|png';
    $config['upload_max_size'] = '1000';


==============================================================
 function for upload
==============================================================
<?php
public function upload_gambar()
{
    $config['upload_path'] = $this->config->item('upload_path');
    $config['allowed_types'] = $this->config->item('upload_tipe');
    $config['max_size'] = $this->config->item('upload_max_size');
    $this->load->library('upload',$config);

    if (!$this->upload->do_upload()) {
       echo $this->upload->display_errors();
    } else {
       $file_data = $this->upload->data();
       $file_path = $this->config->item('upload_path').$file_data['file_name'];
       echo "Sukses upload file: ".$file_data['file_name']."<br />Lokasi file di: ".$file_path;
    }
}


==============================================================
 html & script for upload picture with ajax processing
==============================================================
<?php
     $attributes = array('class' => 'form-upload','enctype' => 'multipart/form-data', 'id' => 'myFRM');
     echo form_open('<<URL_UPLOAD_HERE>>',$attributes);
?>
<div id="pesan"></div>
<span id="loading"></span>
<h2 class="form-signin-heading">Upload gambar</h2>
<div class="form-group">
    <label for="fileinput">File input</label>
    <input type="file" id="fileinput" name="userfile" class="form-control" >
</div>
<button class="btn btn-lg btn-primary btn-block" type="submit" id="btn_upload" class="btn btn-default">Upload</button>
<script>
            $(document).ready(function() {
                $("#myFRM").on('submit',(function(e) {
                    e.preventDefault();
                    $.ajax({
                        url: "<<URL_UPLOAD_HERE>>",
                        type: "POST",
                        data: new FormData(this),
                        mimeType:"multipart/form-data",
                        contentType: false,
                        cache: false,
                        processData:false,
                        beforeSend:function()
                        {
                            $("#pesan").hide();
                            $("#loading").html('Processing upload file...Please wait...');
                        },
                        complete:function()
                        {
                            $("#loading").empty();
                            $("#pesan").show();
                        },
                        error: function()
                        {
                            $('#pesan').html('Error, unknown');
                        },
                        success: function(data)
                        {
                            $("#pesan").html(data);
                        }
                    });
                }));
            });
</script>
</form>