about phosphor pid control package

[James Feist]

>>>>> But one more question I have is that the above code can only check
>>>>> if a
>>> single fan has failed.
>>>>
>>>>> Our project needs to check for dual-fan failures. Do you have any
>>> suggestions for checking the failure of the dual-fan?
>>>>
>>>> I'm not entirely certain what you mean.  You're saying a dual-fan is
>>>> a fan that has two outputs but one input?
>>>
>>> If this is what you mean, on our systems we simply have a tach sensor
>>> per tach in the fan, i.e. fan1a and fan1b. I think the above logic
>>> would work for this issue.
> I think someone may also need to check for one rotor fan fail, I will push the above code into gerrit
> 
>> I'm so sorry to make you misunderstand because of my unclear expression.
>> The "dual-fan" means "Dual rotor fan" , two tachometer output one PWM
>> input.
> Our architecture is that both fan1a and fan1b fail (dual rotor fan failure) and then this situation is identified as one fan fail.
> 
> Would you have any suggestion or idea?

What we have done in the past is used fan redundancy failures for this 
sort of thing. I would suggest monitoring the fan redundancy interface 
for redundancy lost to create failure: 
https://github.com/openbmc/phosphor-dbus-interfaces/blob/master/xyz/openbmc_project/Control/FanRedundancy.interface.yaml

-James