net: eth: altera: Change reset_mac failure message masks from err to dbg

This debug output is not really an error message since mac reset can fail
if the phy clocks are gated, specifically when the phy has been placed in
a powered down or isolation mode. The netdev output masks were changed from
err to dbg, and comments added in the code.
Signed-off-by: NVince Bridgers <vbridger@opensource.altera.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/altera/altera_tse_main.c

@@ -1099,8 +1099,12 @@ static int tse_open(struct net_device *dev)
 
 	spin_lock(&priv->mac_cfg_lock);
 	ret = reset_mac(priv);
+	/* Note that reset_mac will fail if the clocks are gated by the PHY
+	 * due to the PHY being put into isolation or power down mode.
+	 * This is not an error if reset fails due to no clock.
+	 */
 	if (ret)
-		netdev_err(dev, "Cannot reset MAC core (error: %d)\n", ret);
+		netdev_dbg(dev, "Cannot reset MAC core (error: %d)\n", ret);
 
 	ret = init_mac(priv);
 	spin_unlock(&priv->mac_cfg_lock);
@@ -1204,8 +1208,12 @@ static int tse_shutdown(struct net_device *dev)
 	spin_lock(&priv->tx_lock);
 
 	ret = reset_mac(priv);
+	/* Note that reset_mac will fail if the clocks are gated by the PHY
+	 * due to the PHY being put into isolation or power down mode.
+	 * This is not an error if reset fails due to no clock.
+	 */
 	if (ret)
-		netdev_err(dev, "Cannot reset MAC core (error: %d)\n", ret);
+		netdev_dbg(dev, "Cannot reset MAC core (error: %d)\n", ret);
 	priv->dmaops->reset_dma(priv);
 	free_skbufs(dev);