Finally I got approved cable and firmware reported 40gbps link speed immediately. Nice job, Mellanox, on forcing us to buy special expensive cables. I would like to _emphasize_ that the QSFP+ that NIC firmware refused to recognize as 40gig-capable successfully inter-operates with IXIA 40-gigabit protocol validation HW - suggesting that problems with my generic QSFP+/Cables are unlikely. IXIA is very much a reference test equipment that could be trusted.
I don't see any other reason for this Mellanox NIC problem as to lock customers to the expensive cables away from cheaper generic ones.
Our hope is that to be expected soon arrival of Intel XL710 40GigE NIC will make this market more competitive (Intel also had this braindamage of locking to it's own 10gbps transceivers but at least that could be hacked away in the driver)
Regards,
Philip