Discussion Forum—A Way with Words, a fun radio show and podcast about language

Does anyone know the origin of "I ain't mad at it/that" or "I'm not mad at it/that," meaning to really like something? My sister had a friend show her a picture of a new significant other, and when my sister commented on him having a nice smile, the friend replied, "I ain't mad at it."

I was wondering if the origin of this particular use had anything to do with the 2pac Shakur song "I Ain't Mad at Cha" from the 90's. When googling the phrase, most of the results I see reference hip hop lyrics. I thought of the Tupac song because I remember him saying, "I ain't mad at cha, got nothing but love for ya" in the beginning of the song, which seems to communicate that same feeling. Any thoughts?