popup data to edit in ckeditor

i am submitting data using input text box and ckeditor  and i want to popup data to edit in text box and ckeditor but facing errors while do this... please help me...
my view code is:
<?= form_open('admin/update_post'); ?>
<?php //echo form_hidden('author',$this->session->userdata('username'));?>
<div>
<label for="Title">
<span class="required"><h4>Subject</h4></span>

<?= form_input(['name'=>'sub_heading','placeholder'=>'Your Title','tabindex'=>2,'value'=>set_value($post->sub_heading)]); ?>
</label>
</div>


<div>
<label for="content">
<span class="required"><h4>Content</h4></span>

<?php echo $this->ckeditor->editor('sub_desc',@default_value);?>

</label>
</div>
<div>

<!-- <input type="submit" name="sub" id="sub" value="SEND"> -->
<?= form_submit(['name'=>'submit','id'=>'sub','value'=>'POST']); ?>
</div>
<?= form_close(); ?>



Thanks in advance