[coreboot-gerrit] Patch merged into coreboot/master: lenovo/x200, t400: enable C4 cpu low power state

the following patch was just integrated into master:
commit 2a1847ea125b4b867f435635173acb39c9d75292
Author: Arthur Heymans 
Date:   Fri Jun 17 19:06:25 2016 +0200

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

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
    Signed-off-by: Arthur Heymans 
    Reviewed-on: https://review.coreboot.org/15251
    Tested-by: build bot (Jenkins)
    Reviewed-by: Swift Geek
    Reviewed-by: Paul Menzel 
    Reviewed-by: Nico Huber

See https://review.coreboot.org/15251 for details.

-gerrit