Nathaniel L Desimone has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/35165 )
Change subject: arch/x86: Reserve some CAR memory for FSP single stack requirement ......................................................................
Patch Set 10:
(1 comment)
https://review.coreboot.org/c/coreboot/+/35165/9/src/arch/x86/car.ld File src/arch/x86/car.ld:
https://review.coreboot.org/c/coreboot/+/35165/9/src/arch/x86/car.ld@94 PS9, Line 94: #if CONFIG(FSP_USES_CB_STACK)
If this reservation is needed for FSP-T then I think the FSP spec should be fixed. It has no mention of this in the spec, and I don't see why it would.
The FSP heap is not needed until FSP-M. You can see the list of input parameters for FSP-T at the top of https://github.com/tianocore/edk2/blob/master/IntelFsp2Pkg/FspSecCore/Ia32/F...
The FSP StackBase/StackSize (used to be stack + heap, now its only heap) parameters are part of the FSPM_UPD_COMMON structure in https://github.com/tianocore/edk2/blob/master/IntelFsp2Pkg/FspSecCore/Ia32/F...