[RFC] Sensor Value Updated Time

[Amithash Prasad]

Folks,

Redfish recent schema for https://redfish.dmtf.org/schemas/v1/Sensor.v1_11_1.json now allows for ReadingTime to be reported:
                "ReadingTime": {
                    "description": "The date and time that the reading was acquired from the sensor.",
                    "format": "date-time",
                    "longDescription": "This property shall contain the date and time that the reading data was acquired from the sensor.  This value is used to synchronize readings from multiple sensors and does not represent the time at which the resource was accessed.",
                    "readonly": true,
                    "type": [
                        "string",
                        "null"
                    ],
                    "versionAdded": "v1_1_0"
                },

In order to support this, I am intending to add a new property, ValueUpdatedTime to the Sensor Value DBus interface:
https://gerrit.openbmc.org/c/openbmc/phosphor-dbus-interfaces/+/84171

This will be another pervasive change affecting all sensor services to store the timestamp of the last time value was updated and potentially bmcweb to translate this to the date-time format as specified in Redfish.

I would appreciate feedback on this, or if there are other avenues I could explore which could accomplish the same thing with a lesser pervasive change (Not sure if dbus-properties have a changed timestamp like files do).

Thanks,
Amithash