e1000e: disable far-end loopback mode on ESB2

The ESB2 LAN includes a debug feature that enables far-end loopback (FELB)
of the SerDes/Kumeran interface.  This feature is activated when receiving
a sequence of symbols that includes a reserved codeword.  On a perfect
link, FELB would never be activated.  In the presence of bit errors, there
is a very small, but non-zero, probability of FELB being activated.

If the FELB is activated, the SerDes link becomes non-functional and must
be reset.  It could also corrupt the switching tables in the switch since
the ESB2 is transmitting packets with a different source MAC address.

This patch disables the FELB feature.
Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/e1000e/es2lan.c

@@ -836,6 +836,7 @@ static s32 e1000_init_hw_80003es2lan(struct e1000_hw *hw)
 	struct e1000_mac_info *mac = &hw->mac;
 	u32 reg_data;
 	s32 ret_val;
+	u16 kum_reg_data;
 	u16 i;
 
 	e1000_initialize_hw_bits_80003es2lan(hw);
@@ -861,6 +862,13 @@ static s32 e1000_init_hw_80003es2lan(struct e1000_hw *hw)
 	/* Setup link and flow control */
 	ret_val = e1000e_setup_link(hw);
 
+	/* Disable IBIST slave mode (far-end loopback) */
+	e1000_read_kmrn_reg_80003es2lan(hw, E1000_KMRNCTRLSTA_INBAND_PARAM,
+					&kum_reg_data);
+	kum_reg_data |= E1000_KMRNCTRLSTA_IBIST_DISABLE;
+	e1000_write_kmrn_reg_80003es2lan(hw, E1000_KMRNCTRLSTA_INBAND_PARAM,
+					 kum_reg_data);
+
 	/* Set the transmit descriptor write-back policy */
 	reg_data = er32(TXDCTL(0));
 	reg_data = (reg_data & ~E1000_TXDCTL_WTHRESH) |

drivers/net/e1000e/hw.h

@@ -312,6 +312,7 @@ enum e1e_registers {
 #define E1000_KMRNCTRLSTA_DIAG_OFFSET	0x3    /* Kumeran Diagnostic */
 #define E1000_KMRNCTRLSTA_TIMEOUTS	0x4    /* Kumeran Timeouts */
 #define E1000_KMRNCTRLSTA_INBAND_PARAM	0x9    /* Kumeran InBand Parameters */
+#define E1000_KMRNCTRLSTA_IBIST_DISABLE	0x0200 /* Kumeran IBIST Disable */
 #define E1000_KMRNCTRLSTA_DIAG_NELPBK	0x1000 /* Nearend Loopback mode */
 #define E1000_KMRNCTRLSTA_K1_CONFIG	0x7
 #define E1000_KMRNCTRLSTA_K1_ENABLE	0x0002