netdev - [PATCH v2 net] net: stmmac: work around sporadic tx issue on link-up

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Date:   Wed, 24 Aug 2022 22:34:49 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
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>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "moderated list:ARM/STM32 ARCHITECTURE" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Qi Duan <qi.duan@...ogic.com>, Da Xue <da@...sconfused.com>,
        Jerome Brunet <jbrunet@...libre.com>, rayagond@...avyalabs.com,
        Giuseppe Cavallaro <peppe.cavallaro@...com>
Subject: [PATCH v2 net] net: stmmac: work around sporadic tx issue on link-up

This is a follow-up to the discussion in [0]. It seems to me that
at least the IP version used on Amlogic SoC's sometimes has a problem
if register MAC_CTRL_REG is written whilst the chip is still processing
a previous write. But that's just a guess.
Adding a delay between two writes to this register helps, but we can
also simply omit the offending second write. This patch uses the second
approach and is based on a suggestion from Qi Duan.
Benefit of this approach is that we can save few register writes, also
on not affected chip versions.

[0] https://www.spinics.net/lists/netdev/msg831526.html

v2:
- change Fixes tag to the commmit that added stmmac_set_mac() 11yrs ago

Fixes: bfab27a146ed ("stmmac: add the experimental PCI support")
Suggested-by: Qi Duan <qi.duan@...ogic.com>
Suggested-by: Jerome Brunet <jbrunet@...libre.com>
Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
---
 drivers/net/ethernet/stmicro/stmmac/dwmac_lib.c   | 8 ++++++--
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 9 +++++----
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac_lib.c b/drivers/net/ethernet/stmicro/stmmac/dwmac_lib.c
index caa4bfc4c..9b6138b11 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac_lib.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac_lib.c
@@ -258,14 +258,18 @@ EXPORT_SYMBOL_GPL(stmmac_set_mac_addr);
 /* Enable disable MAC RX/TX */
 void stmmac_set_mac(void __iomem *ioaddr, bool enable)
 {
-	u32 value = readl(ioaddr + MAC_CTRL_REG);
+	u32 old_val, value;
+
+	old_val = readl(ioaddr + MAC_CTRL_REG);
+	value = old_val;
 
 	if (enable)
 		value |= MAC_ENABLE_RX | MAC_ENABLE_TX;
 	else
 		value &= ~(MAC_ENABLE_TX | MAC_ENABLE_RX);
 
-	writel(value, ioaddr + MAC_CTRL_REG);
+	if (value != old_val)
+		writel(value, ioaddr + MAC_CTRL_REG);
 }
 
 void stmmac_get_mac_addr(void __iomem *ioaddr, unsigned char *addr,
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 070b5ef16..592d29abc 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -986,10 +986,10 @@ static void stmmac_mac_link_up(struct phylink_config *config,
 			       bool tx_pause, bool rx_pause)
 {
 	struct stmmac_priv *priv = netdev_priv(to_net_dev(config->dev));
-	u32 ctrl;
+	u32 old_ctrl, ctrl;
 
-	ctrl = readl(priv->ioaddr + MAC_CTRL_REG);
-	ctrl &= ~priv->hw->link.speed_mask;
+	old_ctrl = readl(priv->ioaddr + MAC_CTRL_REG);
+	ctrl = old_ctrl & ~priv->hw->link.speed_mask;
 
 	if (interface == PHY_INTERFACE_MODE_USXGMII) {
 		switch (speed) {
@@ -1064,7 +1064,8 @@ static void stmmac_mac_link_up(struct phylink_config *config,
 	if (tx_pause && rx_pause)
 		stmmac_mac_flow_ctrl(priv, duplex);
 
-	writel(ctrl, priv->ioaddr + MAC_CTRL_REG);
+	if (ctrl != old_ctrl)
+		writel(ctrl, priv->ioaddr + MAC_CTRL_REG);
 
 	stmmac_mac_set(priv, priv->ioaddr, true);
 	if (phy && priv->dma_cap.eee) {
-- 
2.37.2