How to restrict field formatter to selected fields?
Use default formatter in your field implemention

$field = array(
  'field_name' =&gt; 'field_csob_srcode',
  'type' =&gt; 'text',
  'settings' =&gt; array(
  'max_length' =&gt; 4,
  ),
  'default_formater' =&gt; 'csob_webpay_description',
);


it should works.