Attention is currently required from: Benjamin Doron, Subrata Banik, Angel Pons, Patrick Rudolph. Nico Huber has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/51205 )
Change subject: soc/intel/skylake: Do not unhide P2SB before disabling HECI ......................................................................
Patch Set 3:
(1 comment)
File src/soc/intel/skylake/finalize.c:
https://review.coreboot.org/c/coreboot/+/51205/comment/6d4206c7_b01561db PS3, Line 37: p2sb_unhide();
There is no "meant to be" that we could trust.
I meant does coreboot intend for P2SB to be hidden while in coreboot and only unhidden when needed, or should it stay visible and be hidden before the OS?
coreboot intends to only hide things when it makes sense, e.g. before jumping to the payload or OS. But Intel doesn't allow what makes sense.
We could define more precise intentions with what is possible in the presence of FSP in mind. But first, somebody would have to analyze the FSP binary to see when it hides things. It's not only specific to the FSP binaries but also to the platforms, e.g. newer than Kaby Lake platforms change to POST_BOOT_SAI very early in the boot process, leaving a mess. Even if you figure out when FSP hides things, it might not be possible to unhide anymore.
There might be one way out to align all the platforms: Do every- thing early and assume the device is hidden and not accessible anymore later. But that again needs at least a look at the indi- vidual FSP UPDs if it's possible to do things early.
But I would much prefer to only make any such changes _after_ FSP has been documented (or been replaced, which seems more likely).
Do either seem likely for the foreseeable future?
Not really. I guess documentation for older (than 6 months) platforms is highly unlikely. And any effort to replace FSP unpredictable (so far only individuals seem interested, no companies).
I guess we could start documenting things on our own. Especially for older platforms it seems unlikely that there will be future updates. So maintaining docs might not be too much effort.
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Nico Huber (Code Review)