Carry forward loss in deferred tax calculation

Pass the following entry to create DTA on current year loss :

Deferred Tax Asset Account..........dr

      To Profit & Loss Account.

However create DTA only if there is reasonable certainity of profit in future. 

on which amount the deferred tax asset to be created? is it only for current year loss or along with carried forward loss also?

If earlier DTL were created than pass below entry for reversal of DTL

DTL a/c Dr.

P&L a/c Cr.

If there is no reversal than pass: DTA to P&L