bnx2x: Check if transceiver implements DDM before access

Some transceivers may comply with SFF-8472 even though they do not
implement the Digital Diagnostic Monitoring (DDM) interface described in
the spec. The existence of such area is specified by the 6th bit of byte
92, set to 1 if implemented.

Currently, without checking this bit, bnx2x fails trying to read sfp
module's EEPROM with the follow message:

ethtool -m enP5p1s0f1
Cannot get Module EEPROM data: Input/output error

Because it fails to read the additional 256 bytes in which it is assumed
to exist the DDM data.

This issue was noticed using a Mellanox Passive DAC PN 01FT738. The EEPROM
data was confirmed by Mellanox as correct and similar to other Passive
DACs from other manufacturers.
Signed-off-by: Mauro S. M. Rodrigues <maurosr@linux.vnet.ibm.com>
Acked-by: Sudarsana Reddy Kalluru <skalluru@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bnx2x/bnx2x_ethtool.c

@@ -1609,7 +1609,8 @@ static int bnx2x_get_module_info(struct net_device *dev,
 	}
 
 	if (!sff8472_comp ||
-	    (diag_type & SFP_EEPROM_DIAG_ADDR_CHANGE_REQ)) {
+	    (diag_type & SFP_EEPROM_DIAG_ADDR_CHANGE_REQ) ||
+	    !(diag_type & SFP_EEPROM_DDM_IMPLEMENTED)) {
 		modinfo->type = ETH_MODULE_SFF_8079;
 		modinfo->eeprom_len = ETH_MODULE_SFF_8079_LEN;
 	} else {

drivers/net/ethernet/broadcom/bnx2x/bnx2x_link.h

@@ -62,6 +62,7 @@
 #define SFP_EEPROM_DIAG_TYPE_ADDR		0x5c
 #define SFP_EEPROM_DIAG_TYPE_SIZE		1
 #define SFP_EEPROM_DIAG_ADDR_CHANGE_REQ		(1<<2)
+#define SFP_EEPROM_DDM_IMPLEMENTED		(1<<6)
 #define SFP_EEPROM_SFF_8472_COMP_ADDR		0x5e
 #define SFP_EEPROM_SFF_8472_COMP_SIZE		1