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diff --git a/roms/skiboot/doc/opal-api/opal-pci-phb-mmio-enable-27.rst b/roms/skiboot/doc/opal-api/opal-pci-phb-mmio-enable-27.rst
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+.. _OPAL_PCI_PHB_MMIO_ENABLE:
+
+OPAL_PCI_PHB_MMIO_ENABLE
+========================
+
+.. code-block:: c
+
+   #define OPAL_PCI_PHB_MMIO_ENABLE		27
+
+   int64_t opal_pci_phb_mmio_enable(uint64_t phb_id, uint16_t window_type,
+                                    uint16_t window_num, uint16_t enable);
+
+.. note:: Appears to be POWER7 p7ioc specific. Likely to be removed soon.
+
+**WARNING:** following documentation is from old sources, and is possibly
+not representative of OPALv3 as implemented by skiboot. This should be
+used as a starting point for full documentation.
+
+
+The host calls this function to enable or disable PHB decode of the PCI IO
+and Memory address spaces below that PHB. Window_num selects an mmio window
+within that address space. Enable set to '1' enables the PHB to decode and
+forward system real addresses to PCI memory, while enable set to '0' disables
+PHB decode and forwarding for the address range defined in a particular MMIO
+window.
+
+Not all PHB hardware may support disabling some or all MMIO windows. OPAL
+returns :ref:`OPAL_UNSUPPORTED` if called to disable an MMIO window for which
+hardware does not support disable. KVM may call this function for all MMIO
+windows and ignore the opal_unsuppsorted return code so long as KVM has
+disabled MMIO to all downstream PCI devices and assured that KVM and OS guest
+partitions cannot issue CI loads/stores to these address spaces from the
+processor (e.g.,via HPT).
+
+OPAL returns :ref:`OPAL_SUCCESS` for calls to OPAL to enable them for PHBs that do
+not support disable.
+
+``phb_id``
+  is the value from the PHB node ibm,opal-phbid property.
+
+``window_type``
+  specifies 32-bit or 64-bit PCI memory
+
+  '0' selects PCI IO Space
+
+  '1' selects 32-bit PCI memory space
+
+  '2' selects 64 bit PCI memory space
+
+``window_num``
+  is the MMIO window number within the specified PCI memory space
+
+``enable``
+  specifies to enable or disable this MMIO window.