lenovo/x200,t400: enable C4 cpu low power state

Hardware / Coreboot - Arthur Heymans [aheymans.xyz] - 26 August 2016 17:15 UTC

This enables the C4 low power state on the lenovo x200 and t400. It's inspired by the thread on the mailinglist: "[coreboot] Lenovo X200 running Coreboot drains 3-4W more power than with Vendor BIOS".

What this does, is to enable a C3 state using MWAIT(C3) request and set the southbridge config c4onc3_enable to automatically upgrade C3 to the lower power C4 state. The latency (0x37) is the same value used by the vendor bios.

With C4 enabled the idle power consumption is about ~2-3W lower.

TEST= build and install on target. Use powertop top to measure power usage. To manually disable c-state to compare them, do (tested on linux 4.4): echo 1 > /sys/devices/system/cpu/cpu*/cpuidle/stateX/disable

Change-Id: I1a1663a7662ebc7157a965667680688ad6a33545

2a1847e lenovo/x200,t400: enable C4 cpu low power state
src/mainboard/lenovo/t400/cstates.c | 5 +++++
src/mainboard/lenovo/t400/devicetree.cb | 2 +-
src/mainboard/lenovo/x200/cstates.c | 5 +++++
src/mainboard/lenovo/x200/devicetree.cb | 2 +-
4 files changed, 12 insertions(+), 2 deletions(-)

Upstream: review.coreboot.org

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