The movie’s framing device is familiar, but works. In 1979, a journalist, Dave (Ewan McGregor), bangs on Miles’s New York brownstone. Dave is a scribbler for Rolling Stone or so he claims, and is here for the story, which is more or less the filmmakers’ and our goal, too. Scuffing around in a bathrobe and dark glasses the sizes of hubcaps, Miles has gone hermit, the Prince of Darkness turned the Prince of Silence. His health is bad and one of his hips is shot, and all the street drugs probably aren’t helping. (By his own account, Davis was at one point snorting four or five grams of coke a day, while smoking four packs of cigarettes. Forget playing — how could he breathe?)

Image Ewan McGregor as a journalist in “Miles Ahead.” Credit... Brian Douglas/Sony Pictures Classics

In narrative terms, Dave the journalist is the streamlined and far more economical version of the reporter in “Citizen Kane” who, after death comes to Charles Foster Kane in his castle, sets the investigation — the biography — in motion. Dave breaches Miles’s Xanadu with a foot in the door, a scene that Mr. Cheadle plays for slapstick-spiked comedy. (Dave ends up inside, Miles out, banging to be let in.) Davis is a monumental figure, but Mr. Cheadle isn’t working in marble. His approach is human-scaled. He lets you see Miles sweat, shows the vanity — Miles primping his hair — panic, drug-hunger, meanness, but also the sly intelligence, pleasure and genius. Miles is modal, as he tells Dave, a nod to the improvisational scale-based jazz exemplified by his landmark record “Kind of Blue.”