As per the Minimum Equipment List (MEL) you cannot dispatch a plane for ETOPS if it has PRIM 1 FAULT (Flight computer fault) However if this fault appears in flight just prior to entering the ETOPS/EDTO segment should you still continue or fly a non ETOPS/EDTO route? Since the MEL is only referred to prior to flight, I cannot refer to this document to justify not flying the ETOPS route. There is a requirement though for twins that all EDTO significant systems should be operational before conducting an ETOPS/EDTO flight. I haven’t seen an EDTO specific significant systems list only the general list published by ICAO which includes almost all the systems of the plane. The question is, would PRIM 1 fault, which was considered a NO GO on the ground still be considered an EDTO significant system in flight wherein it would only result to a loss of a pair of spoilers and computer redundancy? I hope somebody here would share their EDTO significant systems list.
Since you are already airborne, the MMEL doesn't come into it. The system was normal when you dispatched. What applies is the QRH (Quick Reference Handbook). You should look for that particular message in the QRH in the section on status messages (I assume that fault messages are white status messages in Airbus-land).
If there are any restrictions on ETOPS operations with a fault that comes on while airborne, there will be a notation of some kind to that effect, referenced or attached to that message in the QRH, that you have to divert or take some sort of mitigating action before or after entering ETOPS conditions. If not, you're good to go.
The MMEL is based on an analysis of risk exposure related to potential follow-on effects following a departure with a degraded system (that is, a second failure of the remaining component of the system in flight that renders the entire system inoperative or operationally compromised). The risk level prior to departure is higher than the risk level while airborne, because as a general rule, double failures on the same flight are assumed to be extremely improbable.
And, obviously, you should consult with someone in authority at your airline instead of going on the statements of anonymous nobodies on the intertubes...