Infiniband QDR to DDR

I have a bunch of computer with onboard Mellanox ConnectX-2 QDR Infiniband 40Gbps Controllers. They have QSFP connectors.

I have a switch with 24 4x CX4 DDR connectors.

If I buy QSFP to CX4 cables, will the QDR controllers on the computers be able to downscale to DDR, and be able to communicate with (through) the switch?

From serverfault Realn0whereman

• Infiniband should be smart enough to negotiate a compatible data rate; in your case, since your switch is a DDR switch, your IB network will run at DDR rates.

  Realn0whereman : Well, I have alot banking on this, so I'd like more than a "should". But thank you for your answer. I'll try to give mellanox a call, and leave this thread in case anyone else can answer.

  Realn0whereman : Update: I called mellanox and they verified that QDR can downscale to DDR. Success :D now all I need are QSFP to CX4 cables.
  From ryanlim