Which operating system are you using?
About 2-3 years ago (around RHEL/CentOS 6.0 time), I was using Infinihost III cards. From memory, they used the mthca driver (on RHEL/CentOS) at the time.
These days I'm using ConnectX (version 1) cards, which seem to be using mlx4.
I sort of remember reading that the mthca/mlx4 software changed a while ago, with some of the functionality moved around between them. I don't remember the details in any depth though... and I think that might have just been on ESX drivers or something. (unsure, and it's been a long day. )
