Hailu Mergia, a keyboardist and accordion player, was a musical star in Ethiopia in the 1970s, playing in the one of the country’s best-known instrumental groups, Walias Band. He’s been living in the Washington, D.C., area for the past three decades, working as a cabdriver and playing his music at private events. But his music has attracted new attention since the Awesome Tapes From Africa label reissued a pair of his old recordings, which had been hard to find for many years. This past weekend, he played two shows in Chicago as part of World Music Festival Chicago — a wonderful series of free concerts sponsored by the city. I saw Mergia’s performance on Saturday, Sept. 12, at the Promontory in Hyde Park (getting there after Eleventh Dream Day’s show in Andersonville). Backed by bass and drums, Mergia played serpentine melodies on keyboards, accordion and melodica, his face occasionally breaking into a gentle smile as he looked out at the young people dancing in front of the stage to the trio’s lively, alluring rhythms.