phosphor-pid-control: dbus tuning interface

[Jason Ling]

>
>
> This capability already exists if you're using phosphor-pid-control
>
>> with entity manager
>
>> ..
>
>> Entity manager essentially will trigger a reconfigure of
> phosphor-pid-control on every change, so new parameters can be tested.


I see. Let me make sure my mental model is correct.
You can modify PID configuration parameters published by entity-manager via
dbus (is this a separate dbus path/interface than the pid-configuration
interface?).
Entity-manager detects the property change/method call and then updates its
pid-configuration on dbus.
phosphor-pid-control is listening on a signal/event and then essentially
restarts itself and picks up the new configuration?


> I'm guessing you didn't know that existed, and clearly Patrick didn't
> either.  So the next question is, where did you go to look for this
> kind of thing (ie, where should we document this)?  There might not be
> a perfect place, but hopefully we can make this more clear in the
> future when people have these needs.


I sure didn't, thanks for pointing this out.  As far as documentation
improvements:
How to configure phosphor-pid-control
<https://github.com/openbmc/phosphor-pid-control/blob/master/configure.md>
should
probably mention something about the capability of configuring
phosphor-pid-control via dbus.
As far as dbus pid-tuning goes, I suppose there should be some mention of
it in https://github.com/openbmc/phosphor-pid-control/blob/master/tuning.md ..
I guess something along the lines of "...dbus configuration changes will be
reflected in the operation of phosphor-pid-control.".
Intentionally left a bit vague because it doesn't HAVE to be entity-manager
providing this configuration interface. It could be some other service that
reads a config.json and publishes this information to dbus...
Which brings me to my next question
"Is the PID configuration interface formally defined as part of
phosphor-dbus-interfaces?"


Thanks for the brain-dump Ed, it's making me rethink my approach. Adding
yet another tuning interface has a clear potential to bloat and over
complicate phosphor-pid-control. It seems like even if a system was using
phosphor-hwmon for sensor telemetry monitoring, you could still use
entity-manager just to publish and modify PID configurations.
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