Notion of Flakiness in Sensor Readings

[James Feist]

On 10/12/2018 01:53 PM, Patrick Venture wrote:
> Currently, there are a few approaches in phosphor-hwmon on how to
> handle sensors being present sometimes, or flaky on reads.  We've
> talked in the past about how to handle a read failure that should be
> ignored.  A real failure that is flaky or temporary.
> 
> I was thinking of just adding a property to the Sensor.Value interface
> to report information.  Basically, someone reading the value needs to
> know if it's valid.  The idea of a range check for validity doesn't
> work as cleanly for this specific purpose, in my opinion.  The min/max
> can be used cleanly to determine the linearization though!
> 
> I was thinking perhaps a boolean, that you can check to see if the
> value should be used or trusted.  Then, I thought, perhaps, a enum
> with a series of states, starting with the states of "Valid',
> "Invalid."  Not being able to think of a third state, I fell back onto
> a boolean.

For Valid / Invalid we've produced nan on D-Bus to know that the sensor 
is in an invalid state (like power off for tach values). Although I'm 
not sure how this would be produced using the int64 interface, for the 
double std::nan will go over d-bus correctly.

> 
> Thoughts?
> 
> Patrick
>