[continuation from https://groups.google.com/a/google.com/forum/#!topic/chromeos-firmware/ZsJ5aoei-7I ]

Since we've done all the work to allow updating the legacy firmware section, we should actually use it. We know that all Rambi (BayTrail) and Auron (non-Samus Broadwell) based Chromebooks shipped without functional SeaBIOS, even though we now have updates available to fix that. We just need to add the hash of the current legacy blob as LEGACY_UPGRADE_WHITELIST to the respective firmware ebuild and update the updater image with a newer version.

Since this is a completely different flash section that's not touched by the normal mode boot flow, maybe we can convince the TPMs and QA to allow this update without doing a whole firmware test run again? We could just replace the current stable BCS image with one that has the new legacy section dd'ed on, without uprevving any of the other components. (The current updater aborts early from autoupdate before checking need_update_legacy, but it would be easy to change that to make it only update the legacy section but touch nothing else in that case.)