A good interview with "Hail! Hail! Rock and Roll!" director Taylor Hackford HERE. Hackford also made the great documentary about Muhammad Ali, "When We Were Kings."
"After I did When We Were Kings, I was offered the feature film Ali. I said, "I already did it." There's no movie star bigger than Muhhamad Ali. Same thing with Chuck Berry — nobody is going to be able to play him the way he does. Luckily, with Ray, Jamie Foxx did a brilliant job, so it can happen, but with Kings and Chuck Berry I was lucky enough to get the subjects in their prime."