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+POWER9 Changes to OPAL API
+==========================
+
+This document is a summary of POWER9 changes to the OPAL API over what it
+was for POWER7 and POWER8. As the POWER series of processors (at least up
+to POWER9) require changes in the hypervisor to work on a new processor
+generation, this gives us an opportunity with POWER9 to clean up several
+parts of the OPAL API.
+
+Eventually, when the kernel drops support for POWER8 and before, we can then
+remove the associated kernel code too.
+
+OPAL_REINIT_CPUS
+----------------
+Can now be extended beyond HILE BE/LE bits. If invalid flags are set on
+POWER9, OPAL_UNSUPPORTED will be returned.
+
+Device Tree
+-----------
+
+- ``/ibm,opal/`` compatible property now just lists ``ibm,opal-v3`` and no longer ``ibm,opal-v2`` (power9 and above only)
+- Use only ``stdout-path`` property from POWER9 and above as usage of ``linux,stdout-path`` is deprecated
+- Rename ``fsp-ipl-side`` as ``sp-ipl-side`` in ``/ipl-params``
+- Add interrupt-parent property for ``/ibm,opal/ipmi`` node on POWER9 and above
+  to make use of OPAL irqchip rather than event interface in linux.
+
+TODO
+----
+Things we still have to do for POWER9:
+
+- PCI to use async API rather than returning delays
+- deprecate/remove v1 APIs where there's a V2
+- Fix this FWTS warning: ::
+
+   FAILED [MEDIUM] DeviceTreeBaseDTCWarnings: Test 3, dtc reports warnings from
+   device tree: Warning (reg_format): "reg" property in /ibm,opal/flash@0 has
+   invalid length (8 bytes) (#address-cells == 0, #size-cells == 0)
+
+- Remove mi-version / ml-version from ``/ibm,opal/firmware`` and replace with something better and more portable