In case anyone is interested, I just got SAS2108 based controller (LSI 9280-i4ie) working in IT mode.
I don't have any external devices to test with, but at least internal port disks are detected.
If someone else wants to try it out, here's what I did:
- clean the flash memory with megarec -cleanflash
- read SBR out, change to Fusion mode (change 0xc6 to 0xd6 at location 0x56), write changed SBR to card
Now you can boot Linux and use lsirec to hostboot using latest 9211-8i firmware, after hostboot run rescan, card should be up and running, disks visible and all.
Programming the firmware to flash chip didn't seem to work with either sas2flash or lsiutil, which limited the card usefulness severely, you could hostboot the card every time but that is not compatible with IOMMU.
So to fix that, I programmed the firmware manually to the flash chip with external programmer - and it actually just worked.
Firmware I programmed to the chip was downloaded from IBM M1015 card flashed with 9211-8i firmware using sas2flash -o -uflash command. That card had 16MB flash chip and this 9280 has only 8MB chip and I wasn't sure where the controller would boot from (and didn't want to desolder the flash chip again) so I cut the firmware up and pasted first 1M from the 16MB file, then last 3M and then last 4M again. Now the firmware is copied at 0x1a0000, 0x2e0000, 0x5a0000 and 0x6e0000 and boot blocks are at 0x3e0000 and 0x7e0000.
Now someone just needs to find out a way to program the flash memory without getting it off from the board fist, I didn't find any hints of anyone doing that on the Internet on SAS2108 controllers.
Maybe I'll try next if the IR firmware is compatible...