1 files changed, 99 insertions, 0 deletions
diff --git a/roms/skiboot/doc/device-tree/ibm,opal/sensors.rst b/roms/skiboot/doc/device-tree/ibm,opal/sensors.rst
new file mode 100644
index 000000000..2dbdb8ae1
--- /dev/null
+++ b/roms/skiboot/doc/device-tree/ibm,opal/sensors.rst
@@ -0,0 +1,99 @@
+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.
+
+.. code-block:: dts
+
+  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";
+	};
+    };
+  };