ibm,opal/sensors/ device tree nodes

All sensors of a POWER8 system are made available to the OS in the ibm,opal/sensors/ directory. Each sensor is identified with a node which name follows this pattern :

<resource class name>@<resource identifier>/

For example :

core-temp@20/

Each node has a minimum set of properties describing the sensor :

• a “compatible” property which should be “ibm,opal-sensor”

• a “sensor-type” property, which can be “temp”, “fan”, “power”. More will be added when new resources are supported. This type is used “as is” by the Linux driver to map sensors in the sysfs interface of the hwmon framework of Linux.

• a “sensor-data” property giving a unique handler for the OPAL_SENSOR_READ call to be used by Linux to get the value of a sensor attribute. This value is opaque to the OS but is currently constructed using the following encoding :

  |  Attr. |Fam|Res. |   Resource     |
  | Number |ily|Class|      Id        |
  |--------|---|-----|----------------|
  

  The sensor family (FSP, DTS, etc) is used to dispatch the call to the appriopriate skiboot component.

• a “sensor-status” property giving the state of the sensor. The status bits have the slightly meanings depending on the resource type but testing against 0x6 should raise an alarm.

• an optional “label” property

Each node can have some extra properties depending on the resource they represent. See the tree below for more information.

ibm,opal {
  sensors {

      /*
       * Core temperatures (DTS) nodes.
       *
       * We use the PIR of the core as a resource identifier.
       */
      core-temp@20 {
              compatible = "ibm,opal-sensor";
              name = "core-temp";
              sensor-type = "temp";

              /* Status bits :
               *
               * 0x0003       FATAL
               * 0x0002       CRITICAL
               * 0x0001       WARNING
               */
              sensor-data = <0x00800020>;

              /*
               * These are extra properties to help Linux output.
               */
              ibm,pir = <0x20>;
              label = "Core";
      };

      /*
       * Centaur temperatures (DTS) nodes. Open Power only.
       *
       * We use the PIR of the core as a resource identifier.
       */
      mem-temp@1 {
              compatible = "ibm,opal-sensor";
              name = "mem-temp";
              sensor-type = "temp";

              /* Status bits :
               *
               * 0x0003       FATAL
               * 0x0002       CRITICAL
               * 0x0001       WARNING
               */
              sensor-data = <0x00810001>;

              /*
               * These are extra properties to help Linux output.
               */
              ibm,chip-id = <0x80000001>;
              label = "Centaur";
      };
  };
};