It is believed that all or most T400 laptops are compatible. See notes about CPU compatibility for potential incompatibilities.
There are two possible flash chip sizes for the T400: 4MiB (32Mbit) or 8MiB (64Mbit). This can be identified by the type of flash chip below the palmrest: 4MiB is SOIC-8, 8MiB is SOIC-16.
The T400 laptops come with the ME (and sometimes AMT in addition) before flashing libreboot. Libreboot disables and removes it by using a modified descriptor: see gm45_remove_me.html (contains notes, plus instructions)
Flashing instructions can be found at ../install/#flashrom
It is recommended that you update to the latest EC firmware version. The EC firmware is separate from libreboot, so we don’t actually provide that, but if you still have Lenovo BIOS then you can just run the Lenovo BIOS update utility, which will update both the BIOS and EC version. See:
NOTE: this can only be done when you are using Lenovo BIOS. How to update the EC firmware while running libreboot is unknown. Libreboot only replaces the BIOS firmware, not EC.
Updated EC firmware has several advantages e.g. bettery battery handling.
The T400, when run without CPU microcode updates in coreboot, currently kernel panics if running QEMU with vt-x enabled on 2 cores for the guest. With a single core enabled for the guest, the guest panics (but the host is fine). Working around this in QEMU might be possible; if not, software virtualization should work fine (it’s just slower).
On GM45 hardware (with libreboot), make sure that the kvm and kvm_intel kernel modules are not loaded, when using QEMU.
The following errata datasheet from Intel might help with investigation: http://download.intel.com/design/mobile/specupdt/320121.pdf
The T400 is almost identical to the X200, code-wise. See x200.html.
The coreboot wiki shows how to collect various logs useful in porting to new boards. Following are outputs from the T400:
Copyright © 2015 Leah Rowe firstname.lastname@example.org
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License Version 1.3 or any later version published by the Free Software Foundation with no Invariant Sections, no Front Cover Texts, and no Back Cover Texts. A copy of this license is found in ../fdl-1.3.html
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