netdev - [PATCH RFC net-next 7/7] net: stmmac: explain the phylink_speed_down() call in stmmac

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Message-Id: <E1ugQ38-006KDX-RT@rmk-PC.armlinux.org.uk>
Date: Mon, 28 Jul 2025 16:46:02 +0100
From: "Russell King (Oracle)" <rmk+kernel@...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>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-stm32@...md-mailman.stormreply.com,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	netdev@...r.kernel.org,
	Paolo Abeni <pabeni@...hat.com>
Subject: [PATCH RFC net-next 7/7] net: stmmac: explain the
 phylink_speed_down() call in stmmac_release()

The call to phylink_speed_down() looks odd on the face of it. Add a
comment to explain why this call is there.

Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index f44f8b1b0efa..0da5c29b8cb0 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -4138,8 +4138,13 @@ static int stmmac_release(struct net_device *dev)
 	struct stmmac_priv *priv = netdev_priv(dev);
 	u32 chan;
 
+	/* If the PHY or MAC has WoL enabled, then the PHY will not be
+	 * suspended when phylink_stop() is called below. Set the PHY
+	 * to its slowest speed to save power.
+	 */
 	if (device_may_wakeup(priv->device))
 		phylink_speed_down(priv->phylink, false);
+
 	/* Stop and disconnect the PHY */
 	phylink_stop(priv->phylink);
 	phylink_disconnect_phy(priv->phylink);
-- 
2.30.2