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: NMatt Carlson <mcarlson@broadcom.com>
Reviewed-by: NMichael Chan <mchan@broadcom.com>
Reviewed-by: NBenjamin Li <benli@broadcom.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/tg3.c

@@ -10822,8 +10822,12 @@ static int tg3_run_loopback(struct tg3 *tp, int loopback_mode)
 
 		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;

drivers/net/tg3.h

@@ -2112,6 +2112,9 @@
 
 /* Fast Ethernet Tranceiver definitions */
 #define MII_TG3_FET_PTEST		0x17
+#define  MII_TG3_FET_PTEST_FRC_TX_LINK	0x1000
+#define  MII_TG3_FET_PTEST_FRC_TX_LOCK	0x0800
+
 #define MII_TG3_FET_TEST		0x1f
 #define  MII_TG3_FET_SHADOW_EN		0x0080