I've followed your advice. Indeed, kernel it's rooted. I've installed a stock 9.1.B.0.411.ftf for Xperia TX by flashtool, (without stock kernel), after thatI believe that root is already there. You can try to install superuser from Gplay and use some applications that requires root. Let me know if it is working. Cheers!
your TWRP kernel and super su, and now everything works well on my LT29i rooted!! Thanks once again!