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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Vincent Whitchurch <vincent.whitchurch@axis.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 5.15 127/207] net: stmmac: Avoid DMA_CHAN_CONTROL write if no Split Header support
Date:   Mon,  6 Dec 2021 15:56:21 +0100
Message-Id: <20211206145614.637847627@linuxfoundation.org>
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From: Vincent Whitchurch <vincent.whitchurch@axis.com>

commit f8e7dfd6fdabb831846ab1970a875746559d491b upstream.

The driver assumes that split headers can be enabled/disabled without
stopping/starting the device, so it writes DMA_CHAN_CONTROL from
stmmac_set_features().  However, on my system (IP v5.10a without Split
Header support), simply writing DMA_CHAN_CONTROL when DMA is running
(for example, with the commands below) leads to a TX watchdog timeout.

 host$ socat TCP-LISTEN:1024,fork,reuseaddr - &
 device$ ethtool -K eth0 tso off
 device$ ethtool -K eth0 tso on
 device$ dd if=/dev/zero bs=1M count=10 | socat - TCP4:host:1024
 <tx watchdog timeout>

Note that since my IP is configured without Split Header support, the
driver always just reads and writes the same value to the
DMA_CHAN_CONTROL register.

I don't have access to any platforms with Split Header support so I
don't know if these writes to the DMA_CHAN_CONTROL while DMA is running
actually work properly on such systems.  I could not find anything in
the databook that says that DMA_CHAN_CONTROL should not be written when
the DMA is running.

But on systems without Split Header support, there is in any case no
need to call enable_sph() in stmmac_set_features() at all since SPH can
never be toggled, so we can avoid the watchdog timeout there by skipping
this call.

Fixes: 8c6fc097a2f4acf ("net: stmmac: gmac4+: Add Split Header support")
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -5531,8 +5531,6 @@ static int stmmac_set_features(struct ne
 			       netdev_features_t features)
 {
 	struct stmmac_priv *priv = netdev_priv(netdev);
-	bool sph_en;
-	u32 chan;
 
 	/* Keep the COE Type in case of csum is supporting */
 	if (features & NETIF_F_RXCSUM)
@@ -5544,10 +5542,13 @@ static int stmmac_set_features(struct ne
 	 */
 	stmmac_rx_ipc(priv, priv->hw);
 
-	sph_en = (priv->hw->rx_csum > 0) && priv->sph;
+	if (priv->sph_cap) {
+		bool sph_en = (priv->hw->rx_csum > 0) && priv->sph;
+		u32 chan;
 
-	for (chan = 0; chan < priv->plat->rx_queues_to_use; chan++)
-		stmmac_enable_sph(priv, priv->ioaddr, sph_en, chan);
+		for (chan = 0; chan < priv->plat->rx_queues_to_use; chan++)
+			stmmac_enable_sph(priv, priv->ioaddr, sph_en, chan);
+	}
 
 	return 0;
 }