[M] Change in coreboot[main]: soc/intel/xeon_sp: Remove PAM unlock operations

[Arthur Heymans (Code Review)]

Attention is currently required from: Shuo Liu.

Arthur Heymans has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/81349?usp=email )

Change subject: soc/intel/xeon_sp: Remove PAM unlock operations
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Patch Set 15:

(1 comment)

Patchset:

PS15:
> Sure, unlock_pam_region() will route the access to PAM-F segment to DRAM, coreboot places ACPI RSDP lower pointer here, without RSDP pointer, LinuxBoot cannot boot.

there are other ways without having it in lower dram. Linuxboot does not need rsdp in lower menory. https://review.coreboot.org/c/coreboot/+/62574
> In SPR, FSP covered such unlock operations (confirmed from source code), and after removed from coreboot, the coreboot ACPI table can still be accessed by LinuxBoot, hence it proves the removal is okay for SPR. (for GNR, the same).
>
> For the calling site of the unlock in CPX and SKX, it is moved from late romstage and early ramstage, which is close to each other. From the ACPI table write point of view, they are similar. However, only compilation test are executed for SKX and CPX.

There are other uses of PAM like SMP init and smm init. I don't know if the change is fine. My bet would be that fsp-m indeed does not need PAM to point to dram on skx and cpx, but without testing it's hard to know. It would be more prudent to move the call back to romstage on untested platforms.