[coreboot] coreboot on Lenovo T420

[Iru Cai]

Hi,

I installed coreboot on my Lenovo ThinkPad T420 laptop today, and I'd like
to share some experience and hope some one can solve some issues on it.

First, I built the T420s port and flashed it to the T420 laptop.
Fortunately, the laptop could be brought up and boot to Linux. However,
several USB ports didn't function properly(except the one for EHCI debug)
because of the difference between T420s and T420 model. Now I've checked
and used the code from the result generated from autoport, and all the USB
ports work fine.

However, the devicetree.cb file generated from autoport does not work
properly. I use GRUB payload with native graphic init. When I use the T420s
devicetree.cb, it works fine, but with the autoport devicetree.cb, only the
backlight is on and nothing displays. At last I built a kernel for GRUB
payload, and the kernel handled the display properly, then I reflashed
another ROM with flashrom to unbrick my laptop.

So can some one give me some instruction on devicetree.cb file? And another
thing, how can I submit the code to the coreboot repository? Is symlinks to
another source files allowed in the source tree?

Iru Cai