soft power off via IPMI and PLDM

[Andrew Geissler]

The soft power off function is where the BMC tells the BIOS firmware that
a power off has been requested. The BMC then waits for the BIOS to gracefully
shut itself down, and then powers the system off.

We have this implemented using the inband IPMI protocol via
https://github.com/openbmc/phosphor-host-ipmid/tree/master/softoff

We also have this same logic implemented using the PLDM protocol via
https://github.com/openbmc/pldm/tree/master/softoff

I'm wondering if anyone has plans to utilize both of these on a system? For
example scenarios where a system may support different BIOS's that
support different inband protocols?

I'm thinking the easiest solution is a bitbake DISTRO_FEATURES option that
installs one or the other. If we support both, it gets more complicated
because one way or another, they will need to know of each other. i.e. if
the BIOS responds to PLDM, then the PLDM service needs to kill the IPMI
service. The design currently is that they sit in the obmc-host-shutdown at .target
and the power down does not continue until they exit.

Andrew