Hi,
I've been testing the Lenovo T420 port recently, and now I can install an Ivy Bridge processor and run fine on Linux(except some thermal issues). However, the native graphics initialization doesn't work properly before Linux kernel boots. I can see the GRUB interface but it displays bad as if it's on a panel larger than the laptop panel. Then, Linux kernel boots and the graphics become good again. I read some of the i915 driver code of Linux, and saw some code about PCH, so I think this issue has something to do about the southbridge. I don't know if someone has tried using mixed generation of CPU and chipset combination with coreboot before, and I hope this issue can be resolved.
I have pushed the patch that makes coreboot support both SNB and IVB processor for review: http://review.coreboot.org/#/c/12087/
Iru Cai