Add an "i2c" subcommand to cxgbetool. You can use this to read
information from the transceivers connected to the ports of a
cxgbe(4) based card.

cxgbetool t4nex0 i2c <port_id> <dev_addr> <addr> [<count>]

For example:

cxgbetool t4nex0 i2c 0 0xa0 3

0x10 [16]

(As per SFF-8472 the SFP+ module is at 0xa0 and bit 4 in the value at
address 3 indicates it's a 10Gbase-SR module, which it is.)