Jimmy Winfrey has pled guilty to 2 counts of violation of the Street Gang Terrorism and Prevention Act ... this according to new legal docs obtained by TMZ. As part of the deal, prosecutors have dropped a slew of other charges -- 4 counts of violation of the RICO Act, 6 other counts of violation of the Street Gang Terrorism and Prevention Act, 12 counts of aggravated assault, 2 counts of criminal damage to property in the first degree and 1 count of possession of a firearm during the commission of a felony.

He was sentenced to 7 years in prison ... a much lighter sentence than what he got in 2015, when the judge threw the book at him with a 20-year sentence. The Georgia Supreme Court overturned his conviction in 2018 and so the case went back to square 1.

And, get this ... Winfrey got credit for time served and set to be released, but Winfrey's lawyer, Steve Sadow, tells TMZ ... the reason his client hasn't been released involves an unrelated outstanding warrants case. Sadow wants to be clear ... Winfrey entered a special kind of guilty plea where his client maintains his innocence, despite pleading guilty.

As part of the sentence, he's also gotta pay $100k in restitution to Alvin Lewis, the bus driver.

TMZ broke the story ... Alvin accused Birdman and Young Thug of striking secret deals with prosecutors in the case. Alvin had said he found it unusual Cobb County prosecutors described Birdman and YT as co-conspirators in the alleged shooter's indictment but did NOT bring charges against them.

Alvin made no bones about it ... he claimed there was overwhelming evidence of complicity among Winfrey, Birdman and Young Thug ... evidence that includes phone records, recorded confessions, and promises of payment.

Sources close to Birdman had told us the rapper denied any involvement in the case. Young Thug has never commented publicly on the incident.