Chris Brown -- Enters Rehab for Anger Management

Chris Brown has just entered a rehab facility for anger management issues ... presumably to deal with his temper problems and to blunt a possible prison sentence.

Sources tell TMZ ... Brown's attorney, Mark Geragos, just dropped him off at a facility in Malibu. The move doesn't come a day too soon.

We've learned the L.A. County probation department is going full bore in its investigation to determine if Brown violated his probation in the Rihanna case by getting arrested in D.C. over the weekend ... after allegedly punching a guy in the nose.

Sources tell TMZ, Brown flew to L.A. after getting released from the D.C. jail and met with L.A. County Probation Department officials today.

We're told it's likely the Probation Department will determine that Brown violated his probation, and a judge could sentence him to as much as 4 years in prison.

Along with Geragos, we're told his mom and GF Karrueche accompanied Chris to the facility. Geragos and the others went to dinner after dropping Chris off. We asked him about Chris, but he wanted to talk about his meal (see video below).

The rehab move could show a measure of good faith and contrition.