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. phylink_speed_up() is
always called in __stmmac_open(), and already has a comment.

Signed-off-by: Russell King (Oracle) <[email protected]>
Reviewed-by: Andrew Lunn <[email protected]>
Signed-off-by: NipaLocal <nipa@local>

Author: Russell King (Oracle)

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);