This has been commented upon in the past and thrashed out at length in different fora, but I felt compelled to talk about it again. (Almost?) Every A.R.Rahman music score seems to have a song in which the lyrics have two repetitions of the first word or principal refrain. The number and consistency of such occurences is quite startling. By way of examples: Chinna Chinna Aasai, Rukmani Rukmani: Roja, Ghanana Ghanana: Lagaan, Humma Humma, Uyire Uyire: Bombay, Tanha Tanha: Rangeela...: the list is large in number.
I wouldn't know if this is a conscious decision between the lyricists working with this music director, or it is an unconscious expression of what works in the world of popular film music. Is it a spillover of the ad jingle making instincts? Does it contribute to a certain degree of lyrical dumbing down that puts forward catchy, syllable repetitions and alliterations? It does not always indicate dumbing down of course, for I wouldn't consider Thamizha Thamizha (Roja) or Kandukondain Kandukondain to have poor quality lyrics. But it is an interesting aspect to the composer's body of work over a decade that does merit thought.