Hibernate or Shutdown From Suspend

Introduction

This feature extends the battery life of Chrome OS device during prolonged non-use by proactively hibernating or shutting down the device after a configurable time.

Details

Chrome OS devices usually support at least 14 days of standby. Users that return to the device tend to do so in the first 3 days. Thus instead of sitting in standby until the battery is completely discharged, this feature suspends to disk (hibernates) or shuts down the device proactively after spending configured time in standby. This helps in reducing battery degradation due to deep discharge. This can also reduce the frequency of trickle charges during boot.

This flowchart depicts the state machine for shutdown-from-suspend. shutdown-from-suspend flowchart

powerd before every suspend will schedule an alarm (that can wake the system from standby) if one is not already running for lower_power_from_suspend_sec pref. On every resume, powerd identifies if the wake is triggered by the user. If so, powerd stops the alarm and resets the state machine. If not, powerd checks if the timer set above has expired. If the timer has expired, powerd will hibernate the device if supported and not disabled via disable_hibernate, or shut down the device if line power is not connected.

Enabling hibernate or shutdown from suspend on a new device

Make sure Dark Resume is enabled on the device.
Optionally configure disable_hibernate in your boxster config, if hibernate is supported on your device.
Configure lower_power_from_suspend_sec pref for the device.

Debugging hibernate or shutdown from suspend

It's helpful to set a very low value for lower_power_from_suspend_sec, like 30 seconds. Use powerd_dbus_suspend --disable_dark_resume=false to suspend the machine manually. Then examine /var/log/power_manager/powerd.LATEST to see what happened on resume.

Configuring hibernate or shutdown from suspend on a test image

Enable Dark Resume on the test image.
Optionally configure disable_hibernate using the step below. Note that hibernate must already be supported on your machine for this to actually hibernate, which requires more than just this change:

# echo 0 > /var/lib/power_manager/disable_hibernate

Perform the following steps to enable hibernate or shutdown from suspend:

# echo x > /var/lib/power_manager/lower_power_from_suspend_sec
# restart powerd

Disabling hibernate or shutdown from suspend on a test image

Perform the following steps to disable hibernate globally, forcing powerd to use shutdown from suspend only:

# echo 1 > /var/lib/power_manager/disable_hibernate
# restart powerd

Perform the following steps to disable hibernate or shutdown from suspend:

# echo 0 > /var/lib/power_manager/lower_power_from_suspend_sec
# restart powerd