skiboot 6.0.6 release notes

Signed-off-by: Stewart Smith <stewart@linux.ibm.com>
(cherry picked from commit 89160502f3695216e9d801b1e97aeee9188a132e)
Signed-off-by: Stewart Smith <stewart@linux.ibm.com>

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+.. _skiboot-6.0.6:
+
+=============
+skiboot-6.0.6
+=============
+
+skiboot 6.0.6 was released on Thursday July 19th, 2018. It replaces
+:ref:`skiboot-6.0.5` as the current stable release in the 6.0.x series.
+
+It is recommended that 6.0.5 be used instead of any previous 6.0.x version,
+especially in the case where NVLINK2 GPUs and/or Mellanox CX5 adapters are
+being used.
+
+Over :ref:`skiboot-6.0.5` we have several important performance related bug
+fixes and one stability bug fix:
+
+- phb4/CAPI: Reallocate PEC2 DMA-Read engines to improve GPU-Direct bandwidth
+
+  We reallocate additional 16/8 DMA-Read engines allocated to stack0/1
+  on PEC2 respectively. This is needed to improve bandwidth available to
+  the Mellanox CX5 adapter when trying to read GPU memory (GPU-Direct).
+
+  If kernel cxl driver indicates a request to allocate maximum possible
+  DMA read engines when calling enable_capi_mode() and card is attached
+  to PEC2/stack0 slot then we assume its a Mellanox CX5 adapter. We then
+  allocate additional 16/8 extra DMA read engines to stack0 and stack1
+  respectively on PEC2. This is done by populating the
+  XPEC_PCI_PRDSTKOVR and XPEC_NEST_READ_STACK_OVERRIDE as suggested by
+  the h/w team.
+- phb4: Disable nodal scoped DMA accesses when PB pump mode is enabled
+
+  By default when a PCIe device issues a read request via the PHB it is first
+  issued with nodal scope. When accessing GPU memory the NPU does not know at the
+  time of response if the requested memory page is off node or not. Therefore
+  every read of GPU memory by a PHB is retried with larger scope which introduces
+  bandwidth and latency issues.
+
+  On smaller boxes which have pump mode enabled nodal and group scoped reads are
+  treated the same and both types of request are broadcast to one chip. Therefore
+  we can avoid the retry by disabling nodal scope on the PHB for these boxes. On
+  larger boxes nodal (single chip) and group (multiple chip) scoped reads are
+  treated differently. Therefore we avoid disabling nodal scope on large boxes
+  which have pump mode disabled to avoid all PHB requests being broadcast to
+  multiple chips.
+- npu2/hw-procedures: Enable parity and credit overflow checks
+
+  Enable these error checking features by setting the appropriate bits in
+  our one-off initialization of each "NTL Misc Config 2" register.
+
+  The exception is NDL RX parity checking, which should be disabled during
+  the link training procedures.