What is the requirement for submitting a revised workshop paper to a conf in CS?
Depends on the specific workshop and conference.

Some workshops (if they are small events at bigger conferences, and if they don't publish the proceedings) don't count as prior publication, so you can use all the material again.

Some workshops are actually more like a regular conference, but use the name workshop.  So you should treat it as prior publication.

I suspect from your question that it is more the former.  I would suggest asking the papers chair for the conference;  if the workshop is related, they are probably familiar with it.