Index: head/sys/dev/sfxge/common/ef10_nic.c
===================================================================
--- head/sys/dev/sfxge/common/ef10_nic.c
+++ head/sys/dev/sfxge/common/ef10_nic.c
@@ -1288,26 +1288,58 @@
 
 
 /*
- * Table of mapping schemes from port number to the number of the external
- * connector on the board. The external numbering does not distinguish
- * off-board separated outputs such as from multi-headed cables.
+ * Table of mapping schemes from port number to external number.
  *
- * The count of adjacent port numbers that map to each external port
+ * Each port number ultimately corresponds to a connector: either as part of
+ * a cable assembly attached to a module inserted in an SFP+/QSFP+ cage on
+ * the board, or fixed to the board (e.g. 10GBASE-T magjack on SFN5121T
+ * "Salina"). In general:
+ *
+ * Port number (0-based)
+ *     |
+ *   port mapping (n:1)
+ *     |
+ *     v
+ * External port number (normally 1-based)
+ *     |
+ *   fixed (1:1) or cable assembly (1:m)
+ *     |
+ *     v
+ * Connector
+ *
+ * The external numbering refers to the cages or magjacks on the board,
+ * as visibly annotated on the board or back panel. This table describes
+ * how to determine which external cage/magjack corresponds to the port
+ * numbers used by the driver.
+ *
+ * The count of adjacent port numbers that map to each external number,
  * and the offset in the numbering, is determined by the chip family and
  * current port mode.
  *
  * For the Huntington family, the current port mode cannot be discovered,
+ * but a single mapping is used by all modes for a given chip variant,
  * so the mapping used is instead the last match in the table to the full
  * set of port modes to which the NIC can be configured. Therefore the
- * ordering of entries in the the mapping table is significant.
+ * ordering of entries in the mapping table is significant.
  */
-static struct {
+static struct ef10_external_port_map_s {
 	efx_family_t	family;
 	uint32_t	modes_mask;
 	int32_t		count;
 	int32_t		offset;
 }	__ef10_external_port_mappings[] = {
-	/* Supported modes with 1 output per external port */
+	/*
+	 * Modes used by Huntington family controllers where each port
+	 * number maps to a separate cage.
+	 * SFN7x22F (Torino):
+	 *	port 0 -> cage 1
+	 *	port 1 -> cage 2
+	 * SFN7xx4F (Pavia):
+	 *	port 0 -> cage 1
+	 *	port 1 -> cage 2
+	 *	port 2 -> cage 3
+	 *	port 3 -> cage 4
+	 */
 	{
 		EFX_FAMILY_HUNTINGTON,
 		(1 << TLV_PORT_MODE_10G) |
@@ -1316,6 +1348,14 @@
 		1,
 		1
 	},
+	/*
+	 * Modes that on Medford allocate each port number to a separate
+	 * cage.
+	 *	port 0 -> cage 1
+	 *	port 1 -> cage 2
+	 *	port 2 -> cage 3
+	 *	port 3 -> cage 4
+	 */
 	{
 		EFX_FAMILY_MEDFORD,
 		(1 << TLV_PORT_MODE_10G) |
@@ -1323,7 +1363,15 @@
 		1,
 		1
 	},
-	/* Supported modes with 2 outputs per external port */
+	/*
+	 * Modes which for Huntington identify a chip variant where 2
+	 * adjacent port numbers map to each cage.
+	 * SFN7x42Q (Monza):
+	 *	port 0 -> cage 1
+	 *	port 1 -> cage 1
+	 *	port 2 -> cage 2
+	 *	port 3 -> cage 2
+	 */
 	{
 		EFX_FAMILY_HUNTINGTON,
 		(1 << TLV_PORT_MODE_40G) |
@@ -1333,6 +1381,14 @@
 		2,
 		1
 	},
+	/*
+	 * Modes that on Medford allocate 2 adjacent port numbers to each
+	 * cage.
+	 *	port 0 -> cage 1
+	 *	port 1 -> cage 1
+	 *	port 2 -> cage 2
+	 *	port 3 -> cage 2
+	 */
 	{
 		EFX_FAMILY_MEDFORD,
 		(1 << TLV_PORT_MODE_40G) |
@@ -1343,7 +1399,14 @@
 		2,
 		1
 	},
-	/* Supported modes with 4 outputs per external port */
+	/*
+	 * Modes that on Medford allocate 4 adjacent port numbers to each
+	 * connector, starting on cage 1.
+	 *	port 0 -> cage 1
+	 *	port 1 -> cage 1
+	 *	port 2 -> cage 1
+	 *	port 3 -> cage 1
+	 */
 	{
 		EFX_FAMILY_MEDFORD,
 		(1 << TLV_PORT_MODE_10G_10G_10G_10G_Q) |
@@ -1351,6 +1414,14 @@
 		4,
 		1,
 	},
+	/*
+	 * Modes that on Medford allocate 4 adjacent port numbers to each
+	 * connector, starting on cage 2.
+	 *	port 0 -> cage 2
+	 *	port 1 -> cage 2
+	 *	port 2 -> cage 2
+	 *	port 3 -> cage 2
+	 */
 	{
 		EFX_FAMILY_MEDFORD,
 		(1 << TLV_PORT_MODE_10G_10G_10G_10G_Q2),
@@ -1375,7 +1446,7 @@
 
 	if ((rc = efx_mcdi_get_port_modes(enp, &port_modes, &current)) != 0) {
 		/*
-		 * No current port mode information
+		 * No current port mode information (i.e. Huntington)
 		 * - infer mapping from available modes
 		 */
 		if ((rc = efx_mcdi_get_port_modes(enp,
@@ -1392,18 +1463,23 @@
 	}
 
 	/*
-	 * Infer the internal port -> external port mapping from
+	 * Infer the internal port -> external number mapping from
 	 * the possible port modes for this NIC.
 	 */
 	for (i = 0; i < EFX_ARRAY_SIZE(__ef10_external_port_mappings); ++i) {
-		if (__ef10_external_port_mappings[i].family !=
-		    enp->en_family)
+		struct ef10_external_port_map_s *eepmp =
+		    &__ef10_external_port_mappings[i];
+		if (eepmp->family != enp->en_family)
 			continue;
-		matches = (__ef10_external_port_mappings[i].modes_mask &
-		    port_modes);
+		matches = (eepmp->modes_mask & port_modes);
 		if (matches != 0) {
-			count = __ef10_external_port_mappings[i].count;
-			offset = __ef10_external_port_mappings[i].offset;
+			/*
+			 * Some modes match. For some Huntington boards
+			 * there will be multiple matches. The mapping on the
+			 * last match is used.
+			 */
+			count = eepmp->count;
+			offset = eepmp->offset;
 			port_modes &= ~matches;
 		}
 	}