sensor->inventory associations in phosphor-hwmon

[Patrick Venture]

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.

>
> Thanks
> Matt
>