A display controller for a data processing system comprises two sets of display processing units, each set of display processing units comprising an input unit operable to read at least one input surface, a processing unit operable to process one or more input surfaces to generate an output surface, and an output unit operable to provide an output surface for display to a display. The display controller also includes internal data path via which pixel data of a surface may be passed between the sets of display processing units, and a control unit that can selectively activate one or both of the sets of display processing units to process one or more input surfaces to generate one or more output surfaces for display.