linux-kernel - [PATCH net 08/13] net: stmmac: Fix Rx IC bit setting procedure for Rx-mitigation

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Date:   Tue, 14 Mar 2023 01:42:32 +0300
From:   Serge Semin <Sergey.Semin@...kalelectronics.ru>
To:     Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>
CC:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Christian Marangi <ansuelsmth@...il.com>,
        Biao Huang <biao.huang@...iatek.com>,
        Yang Yingliang <yangyingliang@...wei.com>,
        <netdev@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        Jose Abreu <Jose.Abreu@...opsys.com>
Subject: [PATCH net 08/13] net: stmmac: Fix Rx IC bit setting procedure for Rx-mitigation

The WDT-less Rx-traffic mitigation is simple: enable the Rx-descriptor
Completion interrupt only when a particular number of descriptors handled
by the NIC. Alas it's broken now because the data variable rx_count_frames
is always set to zero due to commit 6fa9d691b91a ("net: stmmac: Prevent
divide-by-zero") (++rx_count_frames + rx_coal_frames > rx_coal_frames
always if no overflow happens). So Rx IC will be enabled for each
descriptor as soon as rx_coal_frames is non-zero or there is no Rx WDT
available, which basically disables the Rx-mitigation in the framework of
the number of received frames part. Fix that by discarding the statement:
rx_q->rx_count_frames += priv->rx_coal_frames.

Fixes: 6fa9d691b91a ("net: stmmac: Prevent divide-by-zero")
Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 229f827d7572..32aa7953d296 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -4627,7 +4627,6 @@ static inline void stmmac_rx_refill(struct stmmac_priv *priv, u32 queue)
 		stmmac_refill_desc3(priv, rx_q, p);
 
 		rx_q->rx_count_frames++;
-		rx_q->rx_count_frames += priv->rx_coal_frames[queue];
 		if (rx_q->rx_count_frames > priv->rx_coal_frames[queue])
 			rx_q->rx_count_frames = 0;
 
@@ -4967,7 +4966,6 @@ static bool stmmac_rx_refill_zc(struct stmmac_priv *priv, u32 queue, u32 budget)
 		stmmac_refill_desc3(priv, rx_q, rx_desc);
 
 		rx_q->rx_count_frames++;
-		rx_q->rx_count_frames += priv->rx_coal_frames[queue];
 		if (rx_q->rx_count_frames > priv->rx_coal_frames[queue])
 			rx_q->rx_count_frames = 0;
 
-- 
2.39.2