With a response of 1d, partner may have as little as 6-9 points (minimum responding values).
When you rebid 1s, and partner said 2NT, he showed a two response hand of 10-12 points, just below values for an opening hand, but without four spades, since he didn't raise them. Probably a true balanced NT type hand with 2-3 spades opposite your four, 4-5 diamonds, 2-3 clubs, and the rest hearts.
There is a saying that an opening hand opposite an opening hand can make game. That is true if there is a "fit," and you both have something to spare.
In your case, you have a BARE minimum opening hand with 12 HCP points, and partner is showing a SUB-minimum opening hand of 10-12. You probably have 22-24 between you, and no major suit fit, with NT probably being your best spot. You should stop at 2NT, and hope to make eight tricks. Nine is possible, but a stretch.
With a bit more, say the Q of diamonds opposite his, or AQJTx of clubs instead of what you have, I'd raise to 3NT.