Hi rohit,
enough data in the sense minimum RB to schedule is 1RB, so if you have data below 1 RB then we should make the data to fit in one RB. in this case MAC will do padding to make it 1Rb or any other nearby round offs then it will send as a TB.
Like say e.g RLC has data of 2900 bytes in its buffer, when MAC schedules, it gives grant of 15Rb because 14RB < 2900 < 15RB , say e.g in 15RB you can send 3000 bytes of data then MAC has to do 100bytes of padding.