IPMI sensor names with VMware ESXi. Found the answers.

[Paul Fertser]

Hello,

I've figured out the issues and the fixes, so answering myself here to
get it recorded in the mailing list thread and indexed by the search
engines.

On Mon, Jul 25, 2022 at 04:20:04PM +0300, Paul Fertser wrote:
> We're facing what might be an interoperability issue between OpenBMC
> sensors exposed via IPMI to the host system and VMware ESXi (version
> 7.0u2).
...
> "Unspecified 1" for all the IPMI sensors "captions".

Long story short, I asked ever-helpful neotic on #vmware IRC channel
and he suggested to take a look at libipmi-4.5 (OpenSolaris heritage)
from their "open source" bundle. Writing a test app based on that
reproduced the problem, so debugging became straightforward.

In my testing the "Unspecified" part of the name was the textual
representation of Entity Id (0 by default), 1 was the Entity
Instance. I documented ways to make it specified with intel-ipmi-oem
(or the new dbus-sdr phosphor-host-ipmid support) in another
mail[0]. When using the static yaml sensors description for
phosphor-host-ipmid "entityID" and "entityInstance" keys need to be
set for each sensor individually.

The actual names are ignored as they're transmitted using what IPMI
specification calls a "Unicode" encoding, in this case libipmi returns
an empty string. I fixed [1] it for intel-ipmi-oem by using "8-bit
ASCII + Latin 1" which makes the library copy strings verbatim. If
this is approved I'll send the corresponding change to
phosphor-host-ipmid (to fix both dbus-sdr and static sensorhandler).

[0] https://lists.ozlabs.org/pipermail/openbmc/2022-August/031723.html
[1] https://gerrit.openbmc.org/c/openbmc/intel-ipmi-oem/+/56626

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