phosphor-hwmon: Removal of sensors from dbus

[Matthew Barth]

In regard to the following issue, please provide any feedback or other 
ideas:

https://github.com/openbmc/openbmc/issues/2327

After investigating how hwmon currently handles returned error codes of 
sensors I've come up with a couple ideas where one of them seems to be 
the most optimal choice that I'll describe here (please refer to the 
issue on the other).

Currently there's a configure option, that when enabled, removes a 
sensor from dbus and allows hwmon to continue when an error on reading 
the sensor occurs. I would like to enhance this change to make a hwmon 
config file entry that could be used per sensor of a device that defines 
a comma separated list of what return code(s) would cause that sensor to 
be removed from dbus. This allows the greatest flexibility in handling 
how error codes should be handled for a device's sensor(s).

e.g.

LABEL_temp198 = "gpu0_core_temp"

REMOVERC_temp198 = EAGAIN


In addition to this, it may also be possible to include the changes 
needed where this REMOVERC config entry could be "globally" defined 
where any sensor provided by that device's hwmon config file that 
returns the given error code(s) would be removed from dbus. I have not 
looked into the effort involved with the change described here, but it 
would just be a further enhancement to the one described above.

Thanks,

Matt