Index: head/sys/dev/sfxge/common/efsys.h
===================================================================
--- head/sys/dev/sfxge/common/efsys.h
+++ head/sys/dev/sfxge/common/efsys.h
@@ -287,6 +287,8 @@
 
 #define	EFSYS_OPT_TUNNEL 0
 
+#define	EFSYS_OPT_FW_SUBVARIANT_AWARE 0
+
 /* ID */
 
 typedef struct __efsys_identifier_s	efsys_identifier_t;
Index: head/sys/dev/sfxge/common/efx_check.h
===================================================================
--- head/sys/dev/sfxge/common/efx_check.h
+++ head/sys/dev/sfxge/common/efx_check.h
@@ -377,4 +377,11 @@
 # endif
 #endif /* EFSYS_OPT_TUNNEL */
 
+#if EFSYS_OPT_FW_SUBVARIANT_AWARE
+/* Advertise that the driver is firmware subvariant aware */
+# if !(EFSYS_OPT_MEDFORD2)
+#  error "FW_SUBVARIANT_AWARE requires MEDFORD2"
+# endif
+#endif
+
 #endif /* _SYS_EFX_CHECK_H */
Index: head/sys/dev/sfxge/common/efx_mcdi.c
===================================================================
--- head/sys/dev/sfxge/common/efx_mcdi.c
+++ head/sys/dev/sfxge/common/efx_mcdi.c
@@ -1303,7 +1303,9 @@
 	 * FULL_FEATURED datapath firmware type first and fall backs to
 	 * DONT_CARE datapath firmware type if MC_CMD_DRV_ATTACH fails.
 	 */
-	MCDI_IN_SET_DWORD(req, DRV_ATTACH_IN_NEW_STATE, attach ? 1 : 0);
+	MCDI_IN_POPULATE_DWORD_2(req, DRV_ATTACH_IN_NEW_STATE,
+	    DRV_ATTACH_IN_ATTACH, attach ? 1 : 0,
+	    DRV_ATTACH_IN_SUBVARIANT_AWARE, EFSYS_OPT_FW_SUBVARIANT_AWARE);
 	MCDI_IN_SET_DWORD(req, DRV_ATTACH_IN_UPDATE, 1);
 	MCDI_IN_SET_DWORD(req, DRV_ATTACH_IN_FIRMWARE_ID, enp->efv);