Hello Michal,

The T400 BIOS is in a Pre-UEFI Phoenix FFV format. You can use phoenix_extract.py[1] to extract modules from it.

To go back to Lenovo BIOS you can try the following:

1) download an update from lenovo (e.g. 7uuj49us.exe)
2) unpack it with innounp
3a) take the FL2 file (e.g. $01B8100.FL2),  cut out from 0x200000 to 0x400000 and use the resulting image to replace coreboot in the BIOS region (end of flash).
3b) take the FL1 file  (e.g. $01B8100.FL1), unpack it with bcpvd from [1] and flash the result (it's a complete flash image with descriptor and ME) after cutting it at 0x400000
4) according to the descriptor in unpacked FL1 , the GbE region is at 001F6000 - 001F7FFF, so that's the most likely place for storing the MAC address. I'm not sure why your desc.rom lists 5F6000 - 005F7FFF... I think that's outside the flash chip.

[1]: https://github.com/coreboot/bios_extract

-- 
WBR,
 Igor                            mailto:roxfan@skynet.be