sensor->inventory associations in phosphor-hwmon

[James Feist]

On 2/20/19 10:32 AM, Patrick Venture wrote:
> On Wed, Feb 20, 2019 at 10:31 AM Matt Spinler <mspinler at linux.ibm.com> wrote:
>>
>> Hi,
>>
>> We have a need to know which sensor objects hosted by the various
>> phosphor-hwmon
>> daemons belong to which inventory objects.  For example, we need to know
>> that
>> the /xyz/openbmc_project/sensors/power/ps1_input_power sensor belongs to
>> the
>> /xyz/openbmc_project/inventory/system/powersupply1 item.
>>
>> To accomplish this, I am proposing we add a new environment variable to
>> the
>> system specific phosphor-hwmon config files that the phosphor-hwmon code
>> can then use to create associations interfaces that will cause the
>> mapper to
>> create the appropriate association D-Bus paths.
>>
>> As an example, we could add to the power-supply1 conf file an
>> ASSOCIATIONS
>> variable for each sensor (assuming ps1_input_power is represented by
>> IN1):
>>
>>       ASSOCIATIONS_IN1=/xyz/openbmc_project/inventory/system/powersupply1
>>
>> The code would then see that and create a new org.openbmc.Associations
>> interface
>> on the /xyz/openbmc_project/sensors/power/ps1_input_power path with an
>> associations property of:
>>
>>       ["inventory",
>>        "sensors",
>>        "/xyz/openbmc_project/inventory/system/powersupply1"]
>>
>> This leads to the mapper creating:
>>
>>       /xyz/openbmc_project/sensors/power/ps1_input_power/inventory
>>
>> With an xyz.openbmc_project.Association interface with an
>> endpoints property of:
>>
>>       ["/xyz/openbmc_project/inventory/system/powersupply1"]
>>
>> And also the other association path:
>>
>>       /xyz/openbmc_project/inventory/system/powersupply1/sensors
>>
>> With an xyz.openbmc_project.Association interface with an
>> endpoints property of:
>>
>>       ["/xyz/openbmc_project/sensors/power/ps1_input_power"]
>>
>> This now allows one to both find all sensors associated with a power
>> supply, and
>> find which inventory item is associated with a particular sensor.  Note
>> that
>> the endpoints property is an array, and can get entries from multiple
>> places.
>>
>> I suppose we could also put the forward/reverse association names, in
>> this case
>> "inventory" and "sensors", into the hwmon config file, and also allow
>> creating
>> multiple associations for each sensor if there is a usecase, though I
>> would like
>> to keep it as simple as possible:
>>
>> ASSOCIATIONS1_IN1=inventory,sensors,/xyz/openbmc_project/inventory/system/powersupply1
>> ASSOCIATIONS2_IN1=chassis,contained_sensors,/xyz/openbmc_project/inventory/system/chassis
>>
>> What does everyone think?
> 
> I think it's useful and straightforward to use, and easy to test.

Have we considered the alternative of the inventory item creating the 
association? I only ask because in the past we've tried to keep 
redfish/ipmi specific things outside of the sensors. I think this 
proposal works fine btw, just seems like the alternative would work as 
well and would keep sensors as just 'sensors'.

-James

> 
>>
>> Thanks
>> Matt
>>