netdev - net: stmmac: weirdness in stmmac_hw

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Message-ID: <Z7dVp7_InAHe0q_y@shell.armlinux.org.uk>
Date: Thu, 20 Feb 2025 16:17:43 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>
Cc: Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Emil Renner Berthing <kernel@...il.dk>,
	Eric Dumazet <edumazet@...gle.com>,
	Fabio Estevam <festevam@...il.com>, imx@...ts.linux.dev,
	Inochi Amaoto <inochiama@...il.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Jan Petrous <jan.petrous@....nxp.com>,
	Jon Hunter <jonathanh@...dia.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-stm32@...md-mailman.stormreply.com,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Minda Chen <minda.chen@...rfivetech.com>, netdev@...r.kernel.org,
	NXP S32 Linux Team <s32@....com>, Paolo Abeni <pabeni@...hat.com>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Shawn Guo <shawnguo@...nel.org>,
	Thierry Reding <treding@...dia.com>
Subject: net: stmmac: weirdness in stmmac_hw_setup()

While looking through the stmmac driver, I've come across some
weirdness in stmmac_hw_setup() which looks completely barmy to me.

It seems that it follows the initialisation suggested by Synopsys
(as best I can determine from the iMX8MP documentation), even going
as far as to *enable* transmit and receive *before* the network
device has been administratively brought up. stmmac_hw_setup() does
this:

        /* Enable the MAC Rx/Tx */
        stmmac_mac_set(priv, priv->ioaddr, true);

which sets the TE and RE bits in the MAC configuration register.

This means that if the network link is active, packets will start
to be received and will be placed into the receive descriptors.

We won't transmit anything because we won't be placing packets in
the transmit descriptors to be transmitted.

However, this in stmmac_hw_setup() is just wrong. Can it be deleted
as per the below?

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index c2913f003fe6..d6e492f523f5 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -3493,9 +3493,6 @@ static int stmmac_hw_setup(struct net_device *dev, bool ptp_register)
 		priv->hw->rx_csum = 0;
 	}
 
-	/* Enable the MAC Rx/Tx */
-	stmmac_mac_set(priv, priv->ioaddr, true);
-
 	/* Set the HW DMA mode and the COE */
 	stmmac_dma_operation_mode(priv);
 

-- 
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