Change in coreboot[master]: cpu/x86/smm: Add weak SoC and mainboard init and exit methods

[Raul Rangel (Code Review)]

Attention is currently required from: Martin Roth, Karthik Ramasubramanian, Felix Held.
Hello build bot (Jenkins), Martin Roth, Karthik Ramasubramanian, Felix Held,

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/c/coreboot/+/62500

to look at the new patch set (#2).

Change subject: cpu/x86/smm: Add weak SoC and mainboard init and exit methods
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cpu/x86/smm: Add weak SoC and mainboard init and exit methods

This change provides hooks for the SoC and mainboard so they can perform
any initialization and cleanup in the SMM handler.

For example, if we have a UART enabled firmware with DEBUG_SMI, the UART
controller could have been powered off by the OS. In this case we need
to power on the UART when entering SMM, and then power it off before we
exit. If the OS had the UART enabled when entering SMM, we should
snapshot the UART register state, and restore it on exit. Otherwise we
risk clearing some interrupt enable bits.

BUG=b:221231786, b:217968734
TEST=Build test guybrush

Signed-off-by: Raul E Rangel 
Change-Id: I946619cd62a974a98c575a92943b43ea639fc329
---
M src/cpu/x86/smm/smm_module_handler.c
M src/include/cpu/x86/smm.h
2 files changed, 16 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/00/62500/2