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 'Ansuel' Marangi <ansuelsmth@gmail.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index d1a7cf4567bc..a968a13b3183 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -5448,11 +5448,6 @@ static int stmmac_change_mtu(struct net_device *dev, int new_mtu)
 
 	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;
@@ -5466,6 +5461,14 @@ static int stmmac_change_mtu(struct net_device *dev, int new_mtu)
 
 	dev->mtu = mtu;
 
+	if (netif_running(dev)) {
+		netdev_dbg(priv->dev, "restarting interface to change its MTU\n");
+		stmmac_release(dev);
+
+		stmmac_open(dev);
+		stmmac_set_filter(priv, priv->hw, dev);
+	}
+
 	netdev_update_features(dev);
 
 	return 0;
-- 
2.36.1

On Wed, 15 Jun 2022 00:41:41 +0200 Christian 'Ansuel' Marangi wrote:
> +	if (netif_running(dev)) {
> +		netdev_dbg(priv->dev, "restarting interface to change its MTU\n");
> +		stmmac_release(dev);
> +
> +		stmmac_open(dev);
> +		stmmac_set_filter(priv, priv->hw, dev);

What if stmmac_open() fails because the memory is low or is fragmented?

You'd need to invest more effort into this change and try to allocate
all the resources before shutting the device down.

On Wed, Jun 15, 2022 at 07:55:07PM -0700, Jakub Kicinski wrote:
> On Wed, 15 Jun 2022 00:41:41 +0200 Christian 'Ansuel' Marangi wrote:
> > +	if (netif_running(dev)) {
> > +		netdev_dbg(priv->dev, "restarting interface to change its MTU\n");
> > +		stmmac_release(dev);
> > +
> > +		stmmac_open(dev);
> > +		stmmac_set_filter(priv, priv->hw, dev);
> 
> What if stmmac_open() fails because the memory is low or is fragmented?
> 
> You'd need to invest more effort into this change and try to allocate
> all the resources before shutting the device down.

Well what I'm doing here is following what is done with other similar
function in stmmac. For example the reinit_queues and reinit_ringparam
doesn't do such check.

But ok you are right, will see a good solution to change stmmac_open to
preallocate the buffers.

-- 
	Ansuel