Chris Kelly's Wake -- Tears, Forward Pants, Instrumental 'Jump'

Chris Kelly's public wake is under way at a funeral home in Atlanta, GA ... where mourners were greeted with an instrumental version of "Jump" ... TMZ has learned.

Friends and family members have been paying their respects to the Kris Kross rapper at the open-casket event all day long -- while final preparations are made for tomorrow's public funeral.

Although Chris kept faithful to his pants-backward style his entire adult life, his burial trousers were forward ... he was dressed in a black suit, white shirt and pink tie, sporting earrings and a goatee.

We're told Chris "Daddy Mac" Smith and Jermaine Dupri (who discovered Kris Kross) have not arrived to the wake ... yet. Sources tell us Smith is taking Kelly's death especially hard and is still trying to pull himself together.

Inside the casket, on a sign attached to the coffin lid, read the words: "Cause that's what I was born to do ..." lyrics from the Kris Kross hit "Warm It Up."

The casket was flanked by photos of Chris and Daddy Mac in their heyday.

No media were allowed inside, though the viewing was open to the public ... one vehicle rolled up with "Jump" blaring out the windows ... a few local news trucks were parked outside ... but otherwise it's been a quiet affair.

A small group of family and close friends planned to gather later on at Chris's house.

We broke the story ... Kelly died on May 1 after a suspected cocaine and heroin overdose. He was 34.