Merge branch 'mlxsw-Enable-minimum-shaper-on-MC-TCs'

Ido Schimmel says:

====================
mlxsw: Enable minimum shaper on MC TCs

Petr says:

An MC-aware mode was introduced in commit 7b8195306694 ("mlxsw:
spectrum: Configure MC-aware mode on mlxsw ports"). In MC-aware mode,
BUM traffic gets a special treatment by being assigned to a separate set
of traffic classes 8..15. Pairs of TCs 0 and 8, 1 and 9, etc., are then
configured to strictly prioritize the lower-numbered ones. The intention
is to prevent BUM traffic from flooding the switch and push out all UC
traffic, which would otherwise happen, and instead give UC traffic
precedence.

However strictly prioritizing UC traffic has the effect that UC overload
pushes out all BUM traffic, such as legitimate ARP queries. These
packets are kept in queues for a while, but under sustained UC overload,
their lifetime eventually expires and these packets are dropped. That is
detrimental to network performance as well.

In this patchset, MC TCs (8..15) are configured with minimum shaper of
200Mbps (a minimum permitted value) to allow a trickle of necessary
control traffic to get through.

First in patch #1, the QEEC register is extended with fields necessary
to configure the minimum shaper.

In patch #2, minimum shaper is enabled on TCs 8..15.

In patches #3 and #4, first the MC-awareness test is tweaked to support
the minimum shaper, and then a new test is introduced to test that MC
traffic behaves well under UC overload.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>