Nico Huber has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/41471 )
Change subject: soc/intel/broadwell: Mask lower 20 bits of TOLUD and TOLM in systemagent.asl ......................................................................
Patch Set 6:
(1 comment)
https://review.coreboot.org/c/coreboot/+/41471/6/src/soc/intel/broadwell/acp... File src/soc/intel/broadwell/acpi/systemagent.asl:
https://review.coreboot.org/c/coreboot/+/41471/6/src/soc/intel/broadwell/acp... PS6, Line 156: If (Local0 == Local1) {
I don't think any chipset code reserves this region. I don't know why we […]
Thinking further about it, I don't think this reservation is necessary. If we had exactly 4GiB memory installed. ME would cover the space directly below 4GiB. Which includes things that are forwarded to DMI for sure, e.g. ROM and the RCBA which was often at 0xfed1c000.
Intel documentation writers don't seem to know it very well, either. Just saw a memory map chapter in the TGL BIOS Spec, which says all the stolen regions have to be reserved, and the list includes the ME space. That doesn't make any sense in most cases :-/