tg3: Fix AC131 loopback test errors for 5785

The AC131 does not enable the forced transmit clock settings
immediately.  The workaround is to read the register again to get the
setting to take effect.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Reviewed-by: Benjamin Li <benli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/tg3.c b/drivers/net/tg3.c
index cb69679..128126a 100644
--- a/drivers/net/tg3.c
+++ b/drivers/net/tg3.c
@@ -10822,8 +10822,12 @@
 
 		mac_mode = tp->mac_mode & ~MAC_MODE_PORT_MODE_MASK;
 		if (tp->tg3_flags3 & TG3_FLG3_PHY_IS_FET) {
-			if (GET_ASIC_REV(tp->pci_chip_rev_id) == ASIC_REV_5906)
-				tg3_writephy(tp, MII_TG3_FET_PTEST, 0x1800);
+			tg3_writephy(tp, MII_TG3_FET_PTEST,
+				     MII_TG3_FET_PTEST_FRC_TX_LINK |
+				     MII_TG3_FET_PTEST_FRC_TX_LOCK);
+			/* The write needs to be flushed for the AC131 */
+			if (GET_ASIC_REV(tp->pci_chip_rev_id) == ASIC_REV_5785)
+				tg3_readphy(tp, MII_TG3_FET_PTEST, &val);
 			mac_mode |= MAC_MODE_PORT_MODE_MII;
 		} else
 			mac_mode |= MAC_MODE_PORT_MODE_GMII;