peppy: Enable power limiting for thermal control

Hardware / Coreboot - Duncan Laurie [chromium.org] - 6 December 2013 20:28 UTC

Limit power to 12W at 73C and remove limit at 68C.

To have the CPU consume maximum power it is necessary to stress both the CPU and the GPU. Bastion (chrome.supergiantgames.com) and/or webglsamples.googlecode.com can be useful for this.

Testing this properly requires a script to report the running average power readings. The watch_power.sh script is attached to this issue in the partner tracker.

1) Run watch_power.sh continuously: localhost ~ # watch -n 0 bash -e /tmp/watch_power.sh 2) Start Bastion (or other stress apps). The power draw should be close to 15W if under enough load. 3) Watch until temperature climbs above 73C and is caught by the thermal zone 10 second poll, this can be sped up by blocking or removing the fan. 4) The ACPI thermal zone states should change to reflect that active[2] is now enabled and power consumption should drop to 12W. 5) Stop the stress apps and wait until the CPU cools off again, enable the fan again if it was removed. 6) The ACPI thermal zone state should switch back to active[3].

Change-Id: Ie6714a8543d4f06edf8513086fc9c968273bdb23

ddf6890 peppy: Enable power limiting for thermal control
src/mainboard/google/peppy/acpi/thermal.asl | 10 ++++++++--
src/mainboard/google/peppy/acpi_tables.c | 13 ++++++++-----
src/mainboard/google/peppy/thermal.h | 15 +++++----------
3 files changed, 21 insertions(+), 17 deletions(-)

Upstream: review.coreboot.org

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