smsc9420: handle magic field of ethtool_eeprom

ethtool.h says the driver should set the magic field in get_eeprom and
verify it in set_eeprom. This patch adds this functionality using an
arbitary driver-specific magic value constant (0x9420).

Signed-off-by: Steve Glendinning <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/smsc9420.c

···
 	}
 
 	memcpy(data, &eeprom_data[eeprom->offset], len);
+	eeprom->magic = SMSC9420_EEPROM_MAGIC;
 	eeprom->len = len;
 	return 0;
 }
···
 {
 	struct smsc9420_pdata *pd = netdev_priv(dev);
 	int ret;
+
+	if (eeprom->magic != SMSC9420_EEPROM_MAGIC)
+		return -EINVAL;
 
 	smsc9420_eeprom_enable_access(pd);
 	smsc9420_eeprom_send_cmd(pd, E2P_CMD_EPC_CMD_EWEN_);

drivers/net/smsc9420.h

···
 #define LAN_REGISTER_EXTENT		(0x400)
 
 #define SMSC9420_EEPROM_SIZE		((u32)11)
+#define SMSC9420_EEPROM_MAGIC		(0x9420)
 
 #define PKT_BUF_SZ			(VLAN_ETH_FRAME_LEN + NET_IP_ALIGN + 4)