Codeigniter Upload Multiple

<!-- form upload -->
<?php echo $error;?>
<?php echo form_open_multipart('upload/upload');?>
Dokumen : <input type="file" name="dokumen" size="20" /><br>
Foto : <input type="file" name="foto" size="20" />
<br /><br />
<input type="submit" value="upload" />



/**
* Handle form upload
*/
function upload()
{
    $dokumen = $this->do_upload('dokumen');
    $file = $this->do_upload('file');
    $error = [];
    $data = array('upload_dokumen'=>$dokumen['upload_data'], 'upload_file'=>$file['upload_data']);
    if(isset($dokumen[error])){
        $error['error_dokumen'] = $dokumen['error'];
    }
    if(isset($file[error])){
        $error['error_file'] = $file['error'];
    }

    if(isset($error))
        // jika error
        $this->load->view('upload_form', $error);
    }else{
        // jika gak error
        $this->load->view('upload_sukses', $data);
    }
}
function do_upload($file_name)
{

    $this->load->library('upload');

    $config['upload_path'] = './uploads/';
    $config['allowed_types'] = 'doc|docx|pdf|csv';
    $config['max_size'] = '5120000'; // 5MB
    $this->upload->initialize($config); // Important
    $this->upload->do_upload($file_name);


    if (!$this->upload->do_upload())
    {
        $error = array('error' => $this->upload->display_errors());
        return $error;
    }
    else
    {
        $data = array('upload_data' => $this->upload->data());
        return $data;
    }
}