e1000e: disable jumbo frames on 82579 when MACsec enabled in EEPROM

If/when an OEM enables MACsec in the 82579 EEPROM, disable jumbo frames
support in the driver due to an interoperability issue in hardware that
prevents jumbo packets from being transmitted or received.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/e1000e/defines.h

@@ -86,6 +86,7 @@
 #define E1000_CTRL_EXT_IAME           0x08000000 /* Interrupt acknowledge Auto-mask */
 #define E1000_CTRL_EXT_INT_TIMER_CLR  0x20000000 /* Clear Interrupt timers after IMS clear */
 #define E1000_CTRL_EXT_PBA_CLR        0x80000000 /* PBA Clear */
+#define E1000_CTRL_EXT_LSECCK         0x00001000
 #define E1000_CTRL_EXT_PHYPDEN        0x00100000
 
 /* Receive Descriptor bit definitions */

drivers/net/e1000e/ich8lan.c

@@ -758,7 +758,13 @@ static s32 e1000_get_variants_ich8lan(struct e1000_adapter *adapter)
 	if (rc)
 		return rc;
 
-	if (adapter->hw.phy.type == e1000_phy_ife) {
+	/*
+	 * Disable Jumbo Frame support on parts with Intel 10/100 PHY or
+	 * on parts with MACsec enabled in NVM (reflected in CTRL_EXT).
+	 */
+	if ((adapter->hw.phy.type == e1000_phy_ife) ||
+	    ((adapter->hw.mac.type >= e1000_pch2lan) &&
+	     (!(er32(CTRL_EXT) & E1000_CTRL_EXT_LSECCK)))) {
 		adapter->flags &= ~FLAG_HAS_JUMBO_FRAMES;
 		adapter->max_hw_frame_size = ETH_FRAME_LEN + ETH_FCS_LEN;
 	}