This change disables the C1E (Enhanced Halt State) power saving feature
by clearing bit 1 in the MSR_POWER_CTL register. Disabling C1E prevents
the processor from automatically transitioning to a lower
voltage/frequency when all cores are halted, improving deterministic
behaviour.
For this platform, disabling C1E is always required, so the direct MSR
approach avoids FSP reliability issues and configuration complexity
that would come with using the existing devicetree "enable_c1e"
parameter.
TEST=Booted into OS and verified register MSR_POWER_CTL Bit 1 cleared:
- Used rdmsr tool: rdmsr 0x1FC showed bit 1 = 0
- Confirmed across all CPU cores
Change-Id: If076f0bb42f3a0d4b8f895703e88eaf145e4a762
Signed-off-by: Kilian Krause <kilian.krause@siemens.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/88964
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Mario Scheithauer <mario.scheithauer@siemens.com>
9996fc58fd