Redfish BIOS vs. PLDM BIOS

[Andrew Geissler]

We at IBM ran into an issue recently around BIOS entries.

We have a PLDM BIOS entry, pvm_stop_at_standby, which is used to tell the host
whether it should stop in a setup/standby state or continue to boot all the
way up to the operating systems.

We had identified a Redfish API[1] that fit with this function and mapped that
API to a D-Bus property which was then used by PLDM to fill in this BIOS
attribute.

Recently though we've been working on incorporating the bios-settings-mgr into
our code and into PLDM. That provides a generic Redfish API for setting these
BIOS values using key,value pairs.

The issue is that we now have a BIOS value, pvm_stop_at_standby, defined within
this generic schema that should not be set via the Redfish BIOS interface but
instead set via the Systems/system BootSource API we've been using all along.

We've found some other BIOS attributes like this as well, where PLDM has defined
something as a BIOS value but there is a non-BIOS interface in Redfish to
manipulate it. I believe this email thread from Ratan/Manoj is similar [2]

We were brainstorming a bit and the best solution seems to be to break up
the PLDM BIOS values. Either put the one's backed by non-BIOS Redfish API's into
a separate file or name them in a way they can be easily filtered. PLDM then
only reports the real BIOS values to bios-settings-mgr and therefore Redfish
will only shows this as settable via the generic BIOS Redfish interface.
From a host perspective, they all look like BIOS values but how they are set
via Redfish would differ based on the the type of BIOS value noted above.

PLDM would need to support both the generic bios-settings-mgr BIOS values as
well as these other D-Bus backed ones.

Thoughts? Sampa is going to get a discord chat going but there's a lot of
background here so figured I'd send that out via email.

[1]
# pvm_stop_at_standby Enabled
curl -k -H "X-Auth-Token: $TOKEN" -X PATCH https://${BMC_IP}/redfish/v1/Systems/system -d '{"Boot":{"BootSourceOverrideEnabled": "Continuous","BootSourceOverrideTarget": "BiosSetup"}}'

# pvm_stop_at_standby Disabled
curl -k -H "X-Auth-Token: $TOKEN" -X PATCH https://${BMC_IP}/redfish/v1/Systems/system -d '{"Boot":{"BootSourceOverrideEnabled": "Disabled","BootSourceOverrideTarget": "None"}}'

[2]: https://lore.kernel.org/openbmc/b2b4c23a-0be4-8b76-20a2-dc689161490c@linux.vnet.ibm.com/