Hong Kong - Shanghai - USA

I will be flying Hong Kong to Shanghai-PVG on China Eastern and onwards to the USA on Delta 48 hours later. I have booked a hotel for two nights in Shanghai. If I understand the policy correctly, I can transit Shanghai without Visa on a US passport since my stay is 48 hrs. I just apply for transit permit upon arrival at PVG? Do I need to let the airline which will carry me into China know in advance or do I let them know at check-in at Hong Kong?