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+.. _skiboot-5.9-rc5:
+
+skiboot-5.9-rc5
+===============
+
+skiboot v5.9-rc5 was released on Monday October 23rd 2017 approximately
+32,000ft above somewhere north of Tucson, Arizona. It is the fifth
+release candidate of skiboot 5.9, which will become the new stable release
+of skiboot following the 5.8 release, first released August 31st 2017.
+
+skiboot v5.9-rc5 contains all bug fixes as of :ref:`skiboot-5.4.8`
+and :ref:`skiboot-5.1.21` (the currently maintained stable releases). We
+do not currently expect to do any 5.8.x stable releases.
+
+For how the skiboot stable releases work, see :ref:`stable-rules` for details.
+
+The current plan is to cut the final 5.9 very shortly, with skiboot 5.9
+being for all POWER8 and POWER9 platforms in op-build v1.20 (Due October 18th,
+so we're running a bit behind there).
+This release will be targetted to early POWER9 systems.
+
+Over :ref:`skiboot-5.9-rc3`, we have the following changes:
+
+- opal/hmi: Workaround Power9 hw logic bug for couple of TFMR TB errors.
+- opal/hmi: Fix TB reside and HDEC parity error recovery for power9
+- phb4: Escalate freeze to fence to avoid checkstop
+
+  Freeze events such as MMIO loads can cause the PHB to lose it's
+  limited powerbus credits. If all credits are used and a further MMIO
+  will cause a checkstop.
+
+  To work around this, we escalate the troublesome freeze events to a
+  fence. The fence will cause a full PHB reset which resets the powerbus
+  credits and avoids the checkstop.
+- phb4: Update some init registers
+
+  New inits based on next PHB4 workbook. Increases some timeouts to
+  avoid some spurious error conditions.
+- phb4: Enable PHB MMIO in phb4_root_port_init()
+
+  Linux EEH flow is somewhat broken. It saves the PCIe config space of
+  the PHB on boot, which it then uses to restore on EEH recovery. It
+  does this to restore MMIO bars and some other pieces.
+
+  Unfortunately this save is done before any drivers are bound to
+  devices under the PHB. A number of other things are configured in the
+  PHB after drivers start, hence some configuration space settings
+  aren't saved correctly. These include bus master and MMIO bits in the
+  command register.
+
+  Linux tried to hack around this in this linux commit
+  ``bf898ec5cb`` powerpc/eeh: Enable PCI_COMMAND_MASTER for PCI bridges
+  This sets the bus master bit but ignores the MMIO bit.
+
+  Hence we lose MMIO after a full PHB reset. This causes the next MMIO
+  access to the device to fail and for us to perform a PE freeze
+  recovery, which still doesn't set the MMIO bit and hence we still
+  fail.
+
+  This works around this by forcing MMIO on during
+  phb4_root_port_init().
+
+  With this we can recovery from a PHB fence event on POWER9.
+- phb4: Reduce link degraded message log level to debug
+
+  If we hit this message we'll retry and fix the problem. If we run out
+  of retries and can't fix the problem, we'll still print a log message
+  at error level indicating a problem.
+- phb4: Fix GEN3 for DD2.00
+
+  In this fix:
+   62ac7631ae phb4: Fix PCIe GEN4 on DD2.1 and above
+  We fixed DD2.1 GEN4 but broke DD2.00 as GEN3.
+
+  This fixes DD2.00 back to GEN3. This time for sure!