linux-kernel - [PATCH 4.14 91/92] net: stmmac: Set dma ring length before enabling the DMA

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Date:   Thu, 18 Apr 2019 19:57:49 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "peppe.cavallaro@...com, alexandre.torgue@...com, joabreu@...opsys.com,
        Lars Persson" <larper@...s.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Jose Abreu <joabreu@...opsys.com>,
        Lars Persson <larper@...s.com>
Subject: [PATCH 4.14 91/92] net: stmmac: Set dma ring length before enabling the DMA

From: Lars Persson <lars.persson@...s.com>

This was fixed in upstream by commit 7d9e6c5afab6 ("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@...s.com>
Cc: stable@...r.kernel.org # 4.14.x
Cc: Giuseppe Cavallaro <peppe.cavallaro@...com>
Cc: Alexandre Torgue <alexandre.torgue@...com>
Cc: Jose Abreu <joabreu@...opsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -2536,9 +2536,6 @@ static int stmmac_hw_setup(struct net_de
 		netdev_warn(priv->dev, "%s: failed debugFS registration\n",
 			    __func__);
 #endif
-	/* Start the ball rolling... */
-	stmmac_start_all_dma(priv);
-
 	priv->tx_lpi_timer = STMMAC_DEFAULT_TWT_LS;
 
 	if ((priv->use_riwt) && (priv->hw->dma->rx_watchdog)) {
@@ -2558,6 +2555,9 @@ static int stmmac_hw_setup(struct net_de
 			priv->hw->dma->enable_tso(priv->ioaddr, 1, chan);
 	}
 
+	/* Start the ball rolling... */
+	stmmac_start_all_dma(priv);
+
 	return 0;
 }