What is the question form of "used to do"?

What is the correct way to convert "used to do" into a question? Since I want to emphasize that the action is not on-going any more, so simple past tense is not a good idea here. Could I say "do xxx use to do" or "did xxx use to do"? Both sound weird to me.

If there is no way to do it. Do you suggest any other alternatives?

Well, most of your doubts would be retracted after reading up http://www.englishclub.com/grammar/verbs-m_used-to-do.htm

I would like to summarize the main points from the webpage.

1) We use the used to do expression to talk about: - an activity that we did regularly in the past (like a habit) - a situation that was true in the past

For example,

He used to watch a lot of TV.

They used to be married.

2) Used or use? - when there is did in the sentence, we say use to (without d) - when there is no did in the sentence, we say used to (with d)

For example,

Did you use to smoke?

I didn't use to go swimming.

In principle, there's not much reason to think that the construction isn't perfectly regular, and you will find the following used:

Didn't they use to come here often?

But phonetically, "use to" and "used to" are practically indistinguishable and almost certainly not reliably distinguishable. In practice, you will see the following more commonly written down:

Didn't they used to come here often?

In speech, it's not really clear what percentage of people are 'really' saying use and what percentage are saying used.

The following slightly archaic forms also exist:

Used they to help you?

Used they not to help you?

Usen't they to help you?

Of these, usen't they is also used to form tags (albeit not so commonly as other forms such as didn't they, wouldn't they etc).