He is one of my favorites, and I love his playing style.
he says-Tuning your guitar
There are many open tunings you could experiment with but they require you to use your fingers as in normal tuning, this method is very simple and does not require learning countless positions. My way of playing requires very few fingering positions and very little time to learn them so you could be playing the songs you love in a matter of hours.
How I tune
I tune my guitar in an open D tuning, which is in the structure of an E chord, of a correctly tuned guitar. I tune down to the key of D….
D A D F# A D …from top to bottom
Use a tuner or a pitch pipe to help you tune if you do not know anything about musical notes& or a piano will do. Once you have achieved this you are ready to be the next singer / songwriter on your street. Your friends won’t believe it& . That’s the way it happened to me. The main thing is that you have fun doing it.
I have found many of the chords I play, by looking for sounds I liked& you too should not stop at just learning what is on this page. You will discover sounds I have not& i’m sure…
With the following few Chord configurations you will be able to sing thousands of songs… if you want to know that many 
But for now,just learn how to put you fingers… to get the
sounds