Nate DeSimone has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/36328 )
Change subject: [RFC] Documentation/fsp: Discuss FSP-S issues ......................................................................
Patch Set 5:
(1 comment)
https://review.coreboot.org/c/coreboot/+/36328/4/Documentation/fsp/fsp-s_dis... File Documentation/fsp/fsp-s_discussion.md:
https://review.coreboot.org/c/coreboot/+/36328/4/Documentation/fsp/fsp-s_dis... PS4, Line 126: FSP Switches SAI : ----------------
Interesting. While the BIOS Spec doesn't mention any specific point when it should be done, it mentions how to act if it's done after PCI enumeration. That's not part of MRC yet, is it?
The PCI enumeration language is probably discussing the ramifications around 3rd party OpROM dispatch, since that typically happens as part of the PCI enumeration proceedure. The BIOS spec is primarily written by the UEFI team, so yeah we inject some things that make sense as part of the firmware side flow.
If FspmUpd->FspmConfig.MmioSize == 0, then we will count the amount of address space needed to fit all MMIO. This involves a lightweight "PCI enumeration" that counts the amount of address space needed by any PCI devices installed on the system without actually assigning resources or touching the BAR values or trying to setup required alignment. That way the memory map that MRC constructs will be dynamically tailored to work on any system you throw at it automagically.
Also, I don't understand what the fuss is about. It seems most registers are still accessible with SMM_SAI. And let's be honest, if one expects the average IAFW to have SMM secured properly (no exploitable handlers), they probably also believe in fairy tales.
We have been trying to deprecate the "IAFW" term in favor of more generic ones like "system firmware." Personally, I consider "BIOS" to be somewhat of a genericism... kind of like how many people refer to facial tissues as "kleenex" or how searching the Internet is "googling."
We do see a path to SMM being secured on newer platforms with Intel chipsets. We have a new virtualization technology that sandboxes SMM.