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[174.29.1.49]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-8212aa1a2b8sm1792815a34.13.2026.09.30.21.39.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Sep 2026 21:39:24 -0700 (PDT) From: James Hilliard Date: Wed, 30 Sep 2026 22:39:22 -0600 Subject: [PATCH net] net: stmmac: leave the datapath running for normal-size MTU changes MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260930-stmmac-mtu-fastpath-v1-1-fd73f378c071@gmail.com> X-B4-Tracking: v=1; b=H4sIAAAAAAAC/y2NwQ6DIBBEf8XsuSQIFrS/0njYxaVyQC1g08T47 yVtj28mb+aAzClwhltzQOJXyGFdKrSXBtyMy4NFmCqDksrIQUuRS4zoRCy78JjLhmUWpu9bzTh pGiRUc0vsw/u7eoeFC4y/MPFzrw/l3xBmFm6NMZRbg5Y8Ena90qxda65ESsrO2Y69t04OxlhFz sJ4nh/Y9ncutgAAAA== X-Change-ID: 20260930-stmmac-mtu-fastpath-68813ead3b90 To: netdev@vger.kernel.org, Paolo Abeni , Jakub Kicinski , Maxime Chevallier , Andrew Lunn , Eric Dumazet , Maxime Coquelin , Alexandre Torgue , Christian Marangi Cc: "David S. Miller" , linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Eric Dumazet , James Hilliard X-Mailer: b4 0.15.2 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260930_213926_704026_90A9DC17 X-CRM114-Status: GOOD ( 14.43 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 remain on the reopen path until the rollback change. Fixes: 3470079687448 ("net: ethernet: stmicro: stmmac: permit MTU change with interface up") Signed-off-by: James Hilliard --- drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c index 3f34d491c959..03cd14d10356 100644 --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c @@ -6161,7 +6161,12 @@ 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); --- base-commit: a7bfaba4823e3c165bb2004c74eff7c096672bc7 change-id: 20260930-stmmac-mtu-fastpath-68813ead3b90 Best regards, -- James Hilliard