Enabling MMU crashes ARM Cortex A7

I am working on smp_prime code of ARM - A9. And a i want to use that code for cortex A7.

But after making changes like setting smp bit in ACTLR, Making the memory region device and non coherent- then if i enable the MMU bit from system control register. ARM cortex A7 crashes. 

Please give me answer of following questions.

1) Is there any huge bit manipulation required to use same code of A9 for A7 ?

2) What is correct way of enabling MMU ?