Kyösti Mälkki has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/32327 )
Change subject: payload/seabios: Fix CBFS location on APL platform ......................................................................
Patch Set 3:
(1 comment)
https://review.coreboot.org/#/c/32327/3/payloads/external/SeaBIOS/Makefile File payloads/external/SeaBIOS/Makefile:
https://review.coreboot.org/#/c/32327/3/payloads/external/SeaBIOS/Makefile@4... PS3, Line 43: echo "CONFIG_CBFS_LOCATION=0xfffc0000" >> seabios/.config
Well, this is exact the type of problems we run into with hard coding this location. […]
My limited understanding of FMAP/VBOOT2 is that the final flash image file (coreboot.rom) can contain multiple CBFS sections. IMO verified boot flow would dictate that SeaBIOS (or any other payloas) is only allowed to address/access the same CBFS section the payload was loaded from. That would not be a constant you can evaluate build-time.
Maybe it is necessary to add an LB_TAG_ entry to indicate the CBFS master header address with precedence over CONFIG_CBFS_LOCATION in SeaBIOS. Even if SeaBIOS did have FMAP support, you would still need to resolve which CBFS to use.