Song key - I'm Always, by John Frusciante

There is this chord progression used in I’m Always - John Frusciante which I don’t know in which keys it is written:
Dmaj7, C#m7, Bm7, A6
D, C#m, Bm, C, G, F, A, G, F
G, D, Bm, A, G

Can you guys help me figure out in which key this song was written?

The song is in Ab major, at least the versions I found on Youtube. The chords you gave are a step higher (A major). The progression in Roman numerals:

IVmaj7, iii7, ii7, vi7
IV, I6, ii, ♭III, ♭VII, ♭VI, I, ♭VII, ♭VI
IVmaj7/IV, IVmaj7, ii, I, ♭VII

Thank you very much!! But how can I play a IVmaj7/IV?

What do you mean? On an instrument? In Hookpad?

On an instrument. I tried to find on the internet and by myself but I didn’t figured it out.

It’s just a major 7th chord, a fourth above the IV chord. Same thing as a ♭VIImaj7 chord