skiboot 5.9.4 release notes

Signed-off-by: Stewart Smith <[email protected]>

doc/release-notes/skiboot-5.9.4.rst

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+.. _skiboot-5.9.4:
+
+=============
+skiboot-5.9.4
+=============
+
+skiboot 5.9.4 was released on Wednesday November 29th, 2017. It replaces
+:ref:`skiboot-5.9.3` as the current stable release in the 5.9.x series.
+
+Over :ref:`skiboot-5.9.3`, we have one NPU2/NVLink2 fix that works around
+a potential glitch (the one :ref:`skiboot-5.9.3` would hard crash on rather
+than let a system continue to run until it mysteriously crashed later on).
+
+That fix is in two parts:
+
+- npu2: hw-procedures: Change phy_rx_clock_sel values to recover from a
+  potential glitch.
+
+- npu2: hw-procedures: Manipulate IOVALID during training
+
+  Ensure that the IOVALID bit for this brick is raised at the start of
+  link training, in the reset_ntl procedure.
+
+  Then, to protect us from a glitch when the PHY clock turns off or gets
+  chopped, lower IOVALID for the duration of the phy_reset and
+  phy_rx_dccal procedures.