[M] Change in coreboot[main]: cpu/x86/64bit/mode_switch2: The reverse function to mode_switch

[Patrick Rudolph (Code Review)]

Attention is currently required from: Jérémy Compostella, Patrick Rudolph.

Hello Jérémy Compostella, build bot (Jenkins),

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

https://review.coreboot.org/c/coreboot/+/79753?usp=email

to look at the new patch set (#4).

The following approvals got outdated and were removed:
Verified-1 by build bot (Jenkins)

Change subject: cpu/x86/64bit/mode_switch2: The reverse function to mode_switch
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cpu/x86/64bit/mode_switch2: The reverse function to mode_switch

Add another mode_switch assembly function to call x86_64 code from
x86_32 code. This is particullary useful for BLOBs like mrc.bin or
FSP that calls back into coreboot.

The user must first wrap all functions that are to be called from
x86_32 using the macro prot2lm_wrapper. Instead of using the original
function the wrapped functions must be passed to the x86_32 BLOBs.

The assembly code assume that 0-3 32bit arguments are passed to
the wrapped function.

Tested:
- Called x86_64 code from x86_32 code in qemu.
- Booted Lenovo X220 using x86_32 MRC using x86_64 console.

Change-Id: Ib625233e5f673eae9f3dcb2d03004c06bb07b149
Signed-off-by: Patrick Rudolph 
---
M src/cpu/x86/64bit/Makefile.inc
A src/cpu/x86/64bit/mode_switch2.S
A src/cpu/x86/64bit/prot2long.inc
3 files changed, 76 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/53/79753/4