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net: stmmac: leave the datapath running for normal-size MTU changes

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When both MTUs are at most ETH_DATA_LEN, the receive buffer size and MAC
receive limit do not change. Update the MTU without restarting the
datapath.

This also avoids rebinding a live AF_XDP pool to a temporary RXQ. XDP
rejects jumbo MTUs, so all supported XDP MTU changes take this path.
Jumbo transitions still use the existing reopen path.

Found by source review while working on the stmmac MTU/resume recovery
series. The fast path was tested on Allwinner H616 with sun8i EMAC1 and
an AC300 PHY. The AF_XDP scenario was identified by inspection.

Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Reviewed-by: Daniel Machon <daniel.machon@microchip.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20261013-stmmac-mtu-fastpath-v2-1-1e4ce8137689@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
James Hilliard 2026-10-13 11:54:13 -06:00 committed by Paolo Abeni
parent da499b5527
commit d1241cdbbc
1 changed files with 6 additions and 1 deletions
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7
drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
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@ -6265,7 +6265,12 @@ static int stmmac_change_mtu(struct net_device *dev, int new_mtu)
if ((txfifosz < new_mtu) || (new_mtu > BUF_SIZE_16KiB))
return -EINVAL;
if (netif_running(dev)) {
/* Normal-size frames use the same buffers and MAC receive limits.
* In particular, do not disturb a live AF_XDP pool: XDP does not
* support jumbo frames, so it never needs the ring replacement below.
*/
if (netif_running(dev) &&
(dev->mtu > ETH_DATA_LEN || mtu > ETH_DATA_LEN)) {
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);