soc/intel/cannonlake: Allow SoC to choose CAR mode (eNEM/NEM)

This patch avoids cannonlake base config to select eNEM for CAR by
default. Rather allow other SoC config to choose the applicable CAR
mode between eNEM and NEM.

CML and WHL select eNEM whereas CFL decided to use NEM for CAR setup.

Here is some background about why CFL SoC platform decided to choose
NEM over eNEM:

It was found that some coffeelake CPUs like Intel i3 9100E fail to enter
CAR mode because some MSR used by NEM enhanced are lacking. According to
the Intel SDM CPUID.EAX=07h.ECX=0 reg EBX[12 or 15] should indicate the
presence of IA32_PAR_ASSOC and CPUID.EAX=10h.ECX[1 or 2] reg ECX[2]
should indicate IA32_L3_QOS_CFG and IA32_L2_QOS_CFG respectively but
even on a Intel coffeelake CPU that works with the NEM_ENHANCED these
CPUID bits are all 0 so there is no way of knowing whether NEM_ENHANCED
will work at runtime. Instead just always use regular NEM.

Signed-off-by: Subrata Banik <subratabanik@google.com>
Change-Id: Ibeaa4d53279ff9cbcd0b2ac5f2ad71925872355b
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74377
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

0 files changed, 0 insertions, 0 deletions