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+====================================
+Starting and stopping secondary CPUs
+====================================
+
+In this context, each thread is a CPU. That is, you start and stop threads of
+CPUs.
+
+.. _OPAL_START_CPU:
+
+OPAL_START_CPU
+==============
+
+.. code-block:: c
+
+   #define OPAL_START_CPU				41
+
+   int64_t opal_start_cpu_thread(uint64_t server_no, uint64_t start_address);
+
+Returns
+-------
+
+:ref:`OPAL_SUCCESS`
+     The CPU was instructed to start executing instructions from the specified
+     `start_address`.
+     This is an *asynchronous* operation, so it may take a short period of
+     time before the CPU actually starts at that address.
+:ref:`OPAL_PARAMETER`
+     Invalid CPU.
+:ref:`OPAL_WRONG_STATE`
+     If the CPU thread is not in OPAL, or is being re-initialized through :ref:`OPAL_REINIT_CPUS`
+:ref:`OPAL_INTERNAL_ERROR`
+     Something else went horribly wrong.
+
+.. _OPAL_RETURN_CPU:
+
+OPAL_RETURN_CPU
+===============
+
+.. code-block:: c
+
+   #define OPAL_RETURN_CPU				69
+
+   int64_t opal_return_cpu(void);
+
+When OPAL first starts the host, all secondary CPUs are spinning in OPAL.
+To start them, one must call OPAL_START_CPU (you may want to OPAL_REINIT_CPUS
+to set the HILE bit first).
+
+In cases where you need OPAL to do something for you across all CPUs, such
+as OPAL_REINIT_CPUS, (on some platforms) a firmware update or get the machine
+back into a similar state as to when the host OS was started (e.g. for kexec)
+you may also need to return control of the CPU to OPAL.
+
+
+Returns
+-------
+This call does **not return**. You need to OPAL_START_CPU.