On the 2.5.1 it seems that the bus is used for the real time clock (rtc) https://github.com/turing-machines/BMC-Firmware/blob/d9c55b7adaa06ec9abcc707e6a2cc20e1195ee2a/tp2bmc/board/tp2bmc/sun8i-t113s-turing-pi2-v2.5.1.dts#L22