[net-next PATCH RFC 5/5] net: ethernet: stmicro: stmmac: permit MTU change with interface up

[Christian Marangi <ansuelsmth@gmail.com>]

Remove the limitation where the interface needs to be down to change
MTU by releasing and opening the stmmac driver to set the new MTU.
Also call the set_filter function to correctly init the port.
This permits to remove the EBUSY error while the ethernet port is
running permitting a correct MTU change if for example a DSA request
a MTU change for a switch CPU port.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
---
 .../net/ethernet/stmicro/stmmac/stmmac_main.c | 28 +++++++++++++++----
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 330aac10a6e7..2e08be895cde 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -5549,18 +5549,15 @@ static int stmmac_change_mtu(struct net_device *dev, int new_mtu)
 {
 	struct stmmac_priv *priv = netdev_priv(dev);
 	int txfifosz = priv->plat->tx_fifo_size;
+	struct stmmac_dma_conf *dma_conf;
 	const int mtu = new_mtu;
+	int ret;
 
 	if (txfifosz == 0)
 		txfifosz = priv->dma_cap.tx_fifo_size;
 
 	txfifosz /= priv->plat->tx_queues_to_use;
 
-	if (netif_running(dev)) {
-		netdev_err(priv->dev, "must be stopped to change its MTU\n");
-		return -EBUSY;
-	}
-
 	if (stmmac_xdp_is_enabled(priv) && new_mtu > ETH_DATA_LEN) {
 		netdev_dbg(priv->dev, "Jumbo frames not supported for XDP\n");
 		return -EINVAL;
@@ -5572,8 +5569,27 @@ static int stmmac_change_mtu(struct net_device *dev, int new_mtu)
 	if ((txfifosz < new_mtu) || (new_mtu > BUF_SIZE_16KiB))
 		return -EINVAL;
 
-	dev->mtu = mtu;
+	if (netif_running(dev)) {
+		netdev_dbg(priv->dev, "restarting interface to change its MTU\n");
+		/* Try to allocate the new DMA conf with the new mtu */
+		dma_conf = stmmac_setup_dma_desc(priv, mtu);
+		if (IS_ERR(dma_conf)) {
+			netdev_err(priv->dev, "failed allocating new dma conf for new MTU %d\n",
+				   mtu);
+			return PTR_ERR(dma_conf);
+		}
 
+		stmmac_release(dev);
+
+		ret = __stmmac_open(dev, dma_conf);
+		kfree(dma_conf);
+		if (ret) {
+			netdev_err(priv->dev, "failed reopening the interface after MTU change\n");
+			return ret;
+		}
+	}
+
+	dev->mtu = mtu;
 	netdev_update_features(dev);
 
 	return 0;
-- 
2.36.1