Nico Huber has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/40377 )
Change subject: coreboot-id: Add coreboot id based on FMAP entries ......................................................................
Patch Set 2:
Sorry for being late here. Some information from a non-vboot user:
We have our update process in the payload, it checks the id of an image to flash. It's expected at the end of CBFS as it was there for more than a decade (on x86). If we remove it there, we might have to revert this downstream to stay compatible with our current production firmware, but only if we decided to jump to a newer branch for an existing product (unlikely).
Nevertheless, I don't think we should remove this without a more public discussion. There may be more coreboot ecosystem using it than we know.
I haven't looked into the implementation here, but the idea of an FMAP region seems odd: The id section used to contain a version, don't we have multiple versions in one image in case of vboot? Wouldn't that need an FMAP region per RO/RW slot to be consistent?
If we want to unify things, I would propose to put it at the end of each CBFS. So far, every CBFS seems to comprise one version of coreboot. Why at the end? well, it's already there on x86 (non- reset-vector-in-ram case), and I don't expect it to collide in other cases.
Another thought, if we want to get rid of this legacy, x86 location, but keep the id, how about adding a simple file to CBFS as standard from now on, and keeping the legacy id in the bootblock for a few releases until users adapted?