netdev - [PATCH] Revert "net: stmmac: Do not keep rearming the coalesce timer in stmmac

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Date:   Fri, 24 Aug 2018 11:04:40 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Jose Abreu <joabreu@...opsys.com>, netdev@...r.kernel.org
Cc:     Jerome Brunet <jbrunet@...libre.com>, linux-kernel@...r.kernel.org,
        linux-amlogic@...ts.infradead.org,
        Joao Pinto <jpinto@...opsys.com>,
        Vitor Soares <soares@...opsys.com>,
        Corentin Labbe <clabbe@...libre.com>
Subject: [PATCH] Revert "net: stmmac: Do not keep rearming the coalesce timer in stmmac_xmit"

This reverts commit 4ae0169fd1b3c792b66be58995b7e6b629919ecf.

This change in the handling of the coalesce timer is causing regression on
(at least) amlogic platforms.

Network will break down very quickly (a few seconds) after starting
a download. This can easily be reproduced using iperf3 for example.

The problem has been reported on the S805, S905, S912 and A113 SoCs
(Realtek and Micrel PHYs) and it is likely impacting all Amlogics
platforms using Gbit ethernet

No problem was seen with the platform using 10/100 only PHYs (GXL internal)

Reverting change brings things back to normal and allows to use network
again until we better understand the problem with the coalesce timer.

Cc: Jose Abreu <joabreu@...opsys.com>
Cc: Joao Pinto <jpinto@...opsys.com>
Cc: Vitor Soares <soares@...opsys.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@...com>
Cc: Alexandre Torgue <alexandre.torgue@...com>
Cc: Corentin Labbe <clabbe@...libre.com>
Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac.h      | 1 -
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 5 +----
 2 files changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
index 76649adf8fb0..c0a855b7ab3b 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
@@ -112,7 +112,6 @@ struct stmmac_priv {
 	u32 tx_count_frames;
 	u32 tx_coal_frames;
 	u32 tx_coal_timer;
-	bool tx_timer_armed;
 
 	int tx_coalesce;
 	int hwts_tx_en;
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index ff1ffb46198a..9f458bb16f2a 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -3147,16 +3147,13 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 	 * element in case of no SG.
 	 */
 	priv->tx_count_frames += nfrags + 1;
-	if (likely(priv->tx_coal_frames > priv->tx_count_frames) &&
-	    !priv->tx_timer_armed) {
+	if (likely(priv->tx_coal_frames > priv->tx_count_frames)) {
 		mod_timer(&priv->txtimer,
 			  STMMAC_COAL_TIMER(priv->tx_coal_timer));
-		priv->tx_timer_armed = true;
 	} else {
 		priv->tx_count_frames = 0;
 		stmmac_set_tx_ic(priv, desc);
 		priv->xstats.tx_set_ic_bit++;
-		priv->tx_timer_armed = false;
 	}
 
 	skb_tx_timestamp(skb);
-- 
2.17.1