Creating event logs for blackout power losses

[Matt Spinler]

Hi,
We've been asked by field support to create an OpenBMC event log when we 
detect that
we suffered a power blackout, by which I mean the system is up and 
running, and then the
BMC suddenly reboots and when it comes back up main power is off. The 
issue for it is
https://github.com/ibm-openbmc/dev/issues/677.

I have a proposal in there for how to detect it in the chassis state 
manager code, which
basically just consists of persisting the chassis power state and then 
checking it against
the actual value on startup, and an error proposed at
https://gerrit.openbmc-project.xyz/c/openbmc/phosphor-dbus-interfaces/+/22791.

Does anyone have any other ideas or thoughts?  Is it OK if we make this 
the default behavior, or
would it be preferred we enable it with a compile flag?

Thanks,
Matt