[M] Change in coreboot[main]: util/ifdtool: Support the DCI enable bit on Skylake/Kaby Lake

[Máté Kukri (Code Review)]

Attention is currently required from: Angel Pons, Máté Kukri.

Hello build bot (Jenkins),

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

https://review.coreboot.org/c/coreboot/+/82272?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The following approvals got outdated and were removed: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: util/ifdtool: Support the DCI enable bit on Skylake/Kaby Lake
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util/ifdtool: Support the DCI enable bit on Skylake/Kaby Lake

- DCI can also be enabled from firmware via IOSF-SB
  (port 0xb8 byte 4 bit 4).
- Firmware has to set bit 0 of the IA32_DEBUG_INTERFACE
  (0xc80) MSR to consent to the CPU being debugged.
- DCI can be used to debug coreboot either using:
  - SVT CCA adapter (aka blue box)
  - Regular USB3 A-to-A cable with the VCC pin removed
- Setting this bit will cause the ME firmware to enable DCI, before
  the big CPU comes out of reset.
- The file "/home/mca/eom" in the ME's MFS file system has to contain
  b"\x00" for the ME firmware to honor this bit.
  (For DCI enable changing the filesystem is enough, the state of FPFs
   does not matter.)
- Tested on Dell OptiPlex 3050 and Lenovo ThinkPad T480

Change-Id: I242484e7008bb453cb9a0dc186c8a75e6c96e3d3
Signed-off-by: Mate Kukri 
---
M util/ifdtool/ifdtool.c
1 file changed, 99 insertions(+), 30 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/72/82272/4