I have a desktop version and a mobile version of my website. Since the adoption of the mobile version, my adsense earnings were OK for a short period then dropped all the way down to almost $0 RPM. The only thing I could think of is because I didn't give google enough proof that both sites are related.
If I'm not mistaken, I'm supposed to add to the mobile site:
<link rel="canonical" href="desktop.example.com">
And I add this to the desktop site:
<link rel="alternate" href="mobile.example.com">
Is my thinking correct, and is this all I need to eliminate any chance of google believing the two sites are duplicate to each other, or could I add more things as proof?