net: ethernet: davinci_emac: Fix devioctl while in fixed link

BugLink: https://bugs.launchpad.net/bugs/1878232

commit 62522ef3 upstream.

When configured in fixed link, the DaVinci emac driver sets the
priv->phydev to NULL and further ioctl calls to the phy_mii_ioctl()
causes the kernel to crash.

Cc: Brian Hutchinson <b.hutchman@gmail.com>
Fixes: 1bb6aa56 ("net: davinci_emac: Add support for fixed-link PHY")
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ian May <ian.may@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/net/ethernet/ti/davinci_emac.c

@@ -1512,7 +1512,10 @@ static int emac_devioctl(struct net_device *ndev, struct ifreq *ifrq, int cmd)
 
 	/* TODO: Add phy read and write and private statistics get feature */
 
+	if (priv->phydev)
 		return phy_mii_ioctl(priv->phydev, ifrq, cmd);
+	else
+		return -EOPNOTSUPP;
 }
 
 static int match_first_device(struct device *dev, void *data)