The following firmwares are included in v3.6.8010, which is the latest I could find.
Code:
MSX6012F_Ax MT_1270110020 SwitchX-2 based FDR InfiniBand Switch; 12 QSFP ports; Managed ; Subnet Manager for 648 nodes
MSX6012F_WT_Ax MT_1270111029 SwitchX-2 based FDR IB; 12 QSFP ports; Managed ; Subnet Manager for 648 nodes; P1-2 LR4 enabled
MSX6012T_Ax MT_1270110029 SwitchX-2 based FDR10 InfiniBand Switch; 12 QSFP ports; Managed ; Subnet Manager for 648 nodes
MSX6018F-xxxS_Ax MT_1240212020 SwitchX-2 based FDR InfiniBand Switch; 18 QSFP; Managed
MSX6018F-xxxS_WT_Ax MT_1240213020 SwitchX-2 based InfiniBand to Ethernet 1U gateway; 18 QSFP+ ports; PPC460; RoHS6
MSX6018T-xxxS_Ax MT_1240112029 SwitchX-2 based FDR-10 InfiniBand Switch; 18 QSFP; Managed
Note that the _WT_Ax firmware for the SX6012 is the one with LR4 support. Note that the SX6018 has a _WT_Ax firmware too, but the description doesn't mention LR4 (but does mention RoHS6).
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mb300sd Would you be willing to try MT_1240213020 (MSX6018F-xxxS_WT_Ax)?
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MikeWebb Did you confirm that your BiDi transceivers work in both P1 and P2?