Hi, maybe this [URL] could help you.  
Hi Dell team, Could you please advise if we good to rollback or downgrade the bios ?reason because after the upgrade to bios 2.18.1 on OEMR XL R740  and the port went down. Card details is Mellanox ConnectX-5 2x25G (MCX512A-ACAT) The card still detectable.
OEMR XL R740 2.18.1 - how to roll back bios