You do not need the intervention of the server to activate / deactivate a control of the view. Use jquery, which runs on the client, to know when the select
change and if it has the value you need then you enable the inputs, otherwise you disable it:
$("#mi-select").change(function(){
if(this.value == 3){
$(".entradas").attr("disabled", false);
}else{
$(".entradas").attr("disabled", true);
}
})
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select id="mi-select">
<option value="1">Opcion 1</option>
<option value="2">Opcion 2</option>
<option value="3">Opcion 3 y habilita los inputs</option>
<option value="4">Opcion 4</option>
</select>
<div>
<input type="text" disabled placeholder="input 1" class="entradas" />
<input type="text" disabled placeholder="input 2" class="entradas" />
</div>
This gives you the advantage that your page does not have to reload completely to activate / deactivate the inputs.