mlxsw: spectrum: Allow packets to be trapped from any PG

When packets enter the device they are classified to a priority group
(PG) buffer based on their PCP value. After their egress port and
traffic class are determined they are moved to the switch's shared
buffer and await transmission, if:

(Ingress{Port}.Usage < Thres && Ingress{Port,PG}.Usage < Thres &&
 Egress{Port}.Usage < Thres && Egress{Port,TC}.Usage < Thres)
||
(Ingress{Port}.Usage < Min || Ingress{Port,PG} < Min ||
 Egress{Port}.Usage < Min || Egress{Port,TC}.Usage < Min)

Packets scheduled to transmission through CPU port (trapped to CPU) use
traffic class 7, which has a zero maximum and minimum quotas. However,
when such packets arrive from PG 0 they are admitted to the shared
buffer as PG 0 has a non-zero minimum quota.

Allow all packets to be trapped to the CPU - regardless of the PG they
were classified to - by assigning a 10KB minimum quota for CPU port and
TC7.

Fixes: 8e8dfe9f ("mlxsw: spectrum: Add IEEE 802.1Qaz ETS support")
Reported-by: NTamir Winetroub <tamirw@mellanox.com>
Tested-by: NTamir Winetroub <tamirw@mellanox.com>
Signed-off-by: NIdo Schimmel <idosch@mellanox.com>
Signed-off-by: NJiri Pirko <jiri@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/spectrum_buffers.c

@@ -330,7 +330,7 @@ static const struct mlxsw_sp_sb_cm mlxsw_sp_cpu_port_sb_cms[] = {
 	MLXSW_SP_CPU_PORT_SB_CM,
 	MLXSW_SP_CPU_PORT_SB_CM,
 	MLXSW_SP_CPU_PORT_SB_CM,
-	MLXSW_SP_CPU_PORT_SB_CM,
+	MLXSW_SP_SB_CM(MLXSW_SP_BYTES_TO_CELLS(10000), 0, 0),
 	MLXSW_SP_CPU_PORT_SB_CM,
 	MLXSW_SP_CPU_PORT_SB_CM,
 	MLXSW_SP_CPU_PORT_SB_CM,