net: phy: phylink: ensure the carrier is off when starting phylink

[ Upstream commit aeeb2e8fdefdd5d257a1446351c70cb3df540199 ]

Phylink made an assumption about the carrier state being down when
calling phylink_start(). If this assumption isn't satisfied, the
internal phylink state could misbehave and a net device could end up not
being functional.

This patch fixes this by explicitly calling netif_carrier_off() in
phylink_start().

Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/net/phy/phylink.c

@@ -907,6 +907,9 @@ void phylink_start(struct phylink *pl)
 		    phylink_an_mode_str(pl->link_an_mode),
 		    phy_modes(pl->link_config.interface));
 
+	/* Always set the carrier off */
+	netif_carrier_off(pl->netdev);
+
 	/* Apply the link configuration to the MAC when starting. This allows
 	 * a fixed-link to start with the correct parameters, and also
 	 * ensures that we set the appropriate advertisement for Serdes links.