net: stmmac: Set dma ring length before enabling the DMA

This was fixed in upstream by commit 7d9e6c5a ("net: stmmac: Integrate
XGMAC into main driver flow") that is a new feature commit.

We found a race condition in the DMA init sequence that hits if the
PHY already has link up during stmmac_hw_setup. Since the ring length
was programmed after enabling the RX path, we might receive a packet
before the correct ring length is programmed. When that happened we
could not get reliable interrupts for DMA RX and the MTL complained
about RX FIFO overrun.
Signed-off-by: Lars Persson <larper@axis.com>
Cc: stable@vger.kernel.org # 4.9.x
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Cc: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -1747,11 +1747,6 @@ static int stmmac_hw_setup(struct net_device *dev, bool init_ptp)
 	if (ret < 0)
 		pr_warn("%s: failed debugFS registration\n", __func__);
 #endif
-	/* Start the ball rolling... */
-	pr_debug("%s: DMA RX/TX processes started...\n", dev->name);
-	priv->hw->dma->start_tx(priv->ioaddr);
-	priv->hw->dma->start_rx(priv->ioaddr);
-
 	/* Dump DMA/MAC registers */
 	if (netif_msg_hw(priv)) {
 		priv->hw->mac->dump_regs(priv->hw);
@@ -1779,6 +1774,11 @@ static int stmmac_hw_setup(struct net_device *dev, bool init_ptp)
 	if (priv->tso)
 		priv->hw->dma->enable_tso(priv->ioaddr, 1, STMMAC_CHAN0);
 
+	/* Start the ball rolling... */
+	pr_debug("%s: DMA RX/TX processes started...\n", dev->name);
+	priv->hw->dma->start_tx(priv->ioaddr);
+	priv->hw->dma->start_rx(priv->ioaddr);
+
 	return 0;
 }