[Skiboot] skiboot 6.0.6 released!

[Stewart Smith]

skiboot-6.0.6
*************

skiboot 6.0.6 was released on Thursday July 19th, 2018. It replaces
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 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.

-- 
Stewart Smith
OPAL Architect, IBM.