[net-next,mlxsw,0/3] mlxsw: Enable MC-aware mode for mlxsw ports

Message

Petr Machata July 31, 2018, 10:34 a.m. UTC

Due to an issue in Spectrum chips, when unicast traffic shares TC with
BUM traffic, and there is a congestion, the BUM traffic is not dropped
as it should. In order to give unicast traffic precedence over BUM
traffic, configure multicast-aware mode on all ports.

** Note ** I pieced the above from memory, guesswork and Onyx release
   notes. I need to pass it by Matty, but for review of the code here, I
   think it's good enough.

Under multicast-aware regime, when assigning traffic class to a packet,
the switch doesn't merely take the value prescribed by the QTCT
register. For BUM traffic, it instead assigns that value plus 8. That
limits the number of available TCs, but since mlxsw currently only uses
the lower eight anyway, it is no real loss.

The two TCs (UC and MC one) are then mapped to the same subgroup and
strictly prioritized so that UC traffic is preferred in case of
congestion.

In patch #1, introduce a new register, QTCTM, which enables the
multicast-aware mode.

In patch #2, fix a typo in related code.

In patch #3, set up TCs and QTCTM to enable multicast-aware mode.

Petr Machata (3):
  mlxsw: reg: Add QoS Switch Traffic Class Table is Multicast-Aware
    Register
  mlxsw: spectrum: Fix a typo
  mlxsw: spectrum: Configure MC-aware mode on mlxsw ports

 drivers/net/ethernet/mellanox/mlxsw/reg.h      | 37 ++++++++++++++++++++++++++
 drivers/net/ethernet/mellanox/mlxsw/spectrum.c | 26 +++++++++++++++++-
 2 files changed, 62 insertions(+), 1 deletion(-)