sh_eth: Fix crash or memory leak when resizing rings on device that is down

If the device is down then no packet buffers should be allocated.
We also must not touch its registers as it may be powered off.
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/renesas/sh_eth.c

@@ -1976,29 +1976,31 @@ static int sh_eth_set_ringparam(struct net_device *ndev,
 		sh_eth_write(ndev, 0, EDTRR);
 		sh_eth_write(ndev, 0, EDRRR);
 		synchronize_irq(ndev->irq);
-	}
 
-	/* Free all the skbuffs in the Rx queue. */
-	sh_eth_ring_free(ndev);
-	/* Free DMA buffer */
-	sh_eth_free_dma_buffer(mdp);
+		/* Free all the skbuffs in the Rx queue. */
+		sh_eth_ring_free(ndev);
+		/* Free DMA buffer */
+		sh_eth_free_dma_buffer(mdp);
+	}
 
 	/* Set new parameters */
 	mdp->num_rx_ring = ring->rx_pending;
 	mdp->num_tx_ring = ring->tx_pending;
 
-	ret = sh_eth_ring_init(ndev);
-	if (ret < 0) {
-		netdev_err(ndev, "%s: sh_eth_ring_init failed.\n", __func__);
-		return ret;
-	}
-	ret = sh_eth_dev_init(ndev, false);
-	if (ret < 0) {
-		netdev_err(ndev, "%s: sh_eth_dev_init failed.\n", __func__);
-		return ret;
-	}
-
 	if (netif_running(ndev)) {
+		ret = sh_eth_ring_init(ndev);
+		if (ret < 0) {
+			netdev_err(ndev, "%s: sh_eth_ring_init failed.\n",
+				   __func__);
+			return ret;
+		}
+		ret = sh_eth_dev_init(ndev, false);
+		if (ret < 0) {
+			netdev_err(ndev, "%s: sh_eth_dev_init failed.\n",
+				   __func__);
+			return ret;
+		}
+
 		sh_eth_write(ndev, mdp->cd->eesipr_value, EESIPR);
 		/* Setting the Rx mode will start the Rx process. */
 		sh_eth_write(ndev, EDRRR_R, EDRRR);