Lenovo T420 Ivy Bridge Support - i7-3540M

[Cypriot]

In the german forum an user has uploaded a working bios with upgraded intel vbios module ( from the original 2089 version to 2170 ).
According to intel changelog, in version 2113 a new feature was added to vbios:

Cross compatibility feature Implemented with single VBIOS binary to support Both Sandy Bridge and Ivy Bridge platforms with a "chipset selection" option in BMP

Does that mean that the vbios will recognize IVB hardware, or that is a feature that could be enabled with some modifications?
If it' s something related to the problem mentioned in the page of coreboot patch that enable IVB support:

Sandy and Ivy Bridge processors use the same socket,
and a mainboard with the socket can support both types
of CPUs. However, they use different native graphics init
code and cause a crashing if running the wrong code.
So it needs a detecting, then selects the right code to run.

this could be the key feature in order to have IVB cpus working on t420 also with an original bios mod. Am I wrong?

If there is a bios setting to manually select the IVY bridge microcode (CPU and GPU) then I would think this switch from Sandy bridge is possible. The only difference is microcode support and nothing else.