[realtek] Use ID word to detect EEPROM presence

Some onboard RTL8169 NICs seem to leave the EEPROM pins disconnected.
The existing is_valid_ether_addr() test will not necessarily catch
this, since it expects a missing EEPROM to show up as a MAC address of
00:00:00:00:00:00 or ff:ff:ff:ff:ff:ff.  When the EEPROM pins are
floating the MAC address may read as e.g. 00:00:00:00:0f:00, which
will not be detected as invalid.

Check the ID word in the first two bytes of the EEPROM (which should
have the value 0x8129 for all RTL8139 and RTL8169 chips), and use this
to determine whether or not an EEPROM is present.

Reported-by: Carl Karsten <carl@nextdayvideo.com>
Tested-by: Carl Karsten <carl@nextdayvideo.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/realtek.c

  * Initialise EEPROM
  *
  * @v netdev		Network device
+ * @ret rc		Return status code
  */
-static void realtek_init_eeprom ( struct net_device *netdev ) {
+static int realtek_init_eeprom ( struct net_device *netdev ) {
 	struct realtek_nic *rtl = netdev->priv;
+	uint16_t id;
+	int rc;
 
 	/* Initialise SPI bit-bashing interface */
 	rtl->spibit.basher.op = &realtek_basher_ops;
 	}
 	rtl->eeprom.bus = &rtl->spibit.bus;
 
+	/* Check for EEPROM presence.  Some onboard NICs will have no
+	 * EEPROM connected, with the BIOS being responsible for
+	 * programming the initial register values.
+	 */
+	if ( ( rc = nvs_read ( &rtl->eeprom.nvs, RTL_EEPROM_ID,
+			       &id, sizeof ( id ) ) ) != 0 ) {
+		DBGC ( rtl, "REALTEK %p could not read EEPROM ID: %s\n",
+		       rtl, strerror ( rc ) );
+		return rc;
+	}
+	if ( id != cpu_to_le16 ( RTL_EEPROM_ID_MAGIC ) ) {
+		DBGC ( rtl, "REALTEK %p EEPROM ID incorrect (%#04x); assuming "
+		       "no EEPROM\n", rtl, le16_to_cpu ( id ) );
+		return -ENODEV;
+	}
+
 	/* Initialise space for non-volatile options, if available
 	 *
 	 * We use offset 0x40 (i.e. address 0x20), length 0x40.  This
 		nvo_init ( &rtl->nvo, &rtl->eeprom.nvs, RTL_EEPROM_VPD,
 			   RTL_EEPROM_VPD_LEN, NULL, &netdev->refcnt );
 	}
+
+	return 0;
 }
 
 /******************************************************************************
 	realtek_detect ( rtl );
 
 	/* Initialise EEPROM */
-	realtek_init_eeprom ( netdev );
+	if ( ( rc = realtek_init_eeprom ( netdev ) ) == 0 ) {
+
+		/* Read MAC address from EEPROM */
+		if ( ( rc = nvs_read ( &rtl->eeprom.nvs, RTL_EEPROM_MAC,
+				       netdev->hw_addr, ETH_ALEN ) ) != 0 ) {
+			DBGC ( rtl, "REALTEK %p could not read MAC address: "
+			       "%s\n", rtl, strerror ( rc ) );
+			goto err_nvs_read;
+		}
 
-	/* Read MAC address from EEPROM */
-	if ( ( rc = nvs_read ( &rtl->eeprom.nvs, RTL_EEPROM_MAC,
-			       netdev->hw_addr, ETH_ALEN ) ) != 0 ) {
-		DBGC ( rtl, "REALTEK %p could not read MAC address: %s\n",
-		       rtl, strerror ( rc ) );
-		goto err_nvs_read;
-	}
+	} else {
 
-	/* The EEPROM may not be present for onboard NICs.  Fall back
-	 * to reading the current ID register value, which will
-	 * hopefully have been programmed by the platform firmware.
-	 */
-	if ( ! is_valid_ether_addr ( netdev->hw_addr ) ) {
-		DBGC ( rtl, "REALTEK %p seems to have no EEPROM (MAC %s)\n",
-		       rtl, eth_ntoa ( netdev->hw_addr ) );
+		/* EEPROM not present.  Fall back to reading the
+		 * current ID register value, which will hopefully
+		 * have been programmed by the platform firmware.
+		 */
 		for ( i = 0 ; i < ETH_ALEN ; i++ )
 			netdev->hw_addr[i] = readb ( rtl->regs + RTL_IDR0 + i );
 	}

src/drivers/net/realtek.h

 #define RTL_9346CR_EEDI		0x02	/**< Data in */
 #define RTL_9346CR_EEDO		0x01	/**< Data out */
 
+/** Word offset of ID code word within EEPROM */
+#define RTL_EEPROM_ID ( 0x00 / 2 )
+
+/** EEPROM code word magic value */
+#define RTL_EEPROM_ID_MAGIC 0x8129
+
 /** Word offset of MAC address within EEPROM */
 #define RTL_EEPROM_MAC ( 0x0e / 2 )