so, my cards and adapters arrived, nearly finished soldering them all too, so far 3 pairs have been put together for testing and tinkering.
First specimen came with 2.42.5056 HP FW and had link-lights.
Went ahead and flashed a few different cx3 Pro FWs from mellanox because i wasn't really getting the card to work, partially due to stupidity.
I then stumbled upon the cx345A fcCt which appears to be the Pro version to the cx345a fcBt non pros i already have, which would also should be the same Mellanox version of the HP 544+ non flexlom card, so i went ahead and flashed that.
They appear in lspci, mstflint and config find it, i have two ethernet ports.
Everything so good with that so far, except that the ports stay down permanently.
went back and flashed the HP Flexlom FW version 2.35.5100 and the card appears in lspci, mstconfig is not able to read its config "driver might be down or busy" and no eth or ib devices, but a link light without activity.
Looking at /sys/bus/pci/devices/..../ shows no port mode options.
The release-notes of the newest HP 2.42.5700 FW say that having SRIOV enabled on the card and not enabled in the bios keeps the card from working. Maybe tahts the issue here?
EDIT:
My WS stops booting into my Manjaro after flashing the 2.42.5700.
gona try the 2_42_5056 for the hp 544+ non flr again to see if that does anything.
Final: Haven't found any other cards FW to be compatible, though you should test that yourself.
Technically the 544+FLR should work out of the box, i have settled on version 3.42.5700 which has that SRIOV boot failure bug, so right after flashing, you want to use mstconfig to disable sriov.
If the card fails too boot into the OS on your system, well, probably has that issue.