linux-kernel - [PATCH v2 net-next 4/5] net: fec: add change_mtu to support dynamic buffer allocation

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Message-ID: <20250821183336.1063783-5-shenwei.wang@nxp.com>
Date: Thu, 21 Aug 2025 13:33:35 -0500
From: Shenwei Wang <shenwei.wang@....com>
To: Wei Fang <wei.fang@....com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>
Cc: Shenwei Wang <shenwei.wang@....com>,
	Clark Wang <xiaoning.wang@....com>,
	Stanislav Fomichev <sdf@...ichev.me>,
	imx@...ts.linux.dev,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-imx@....com
Subject: [PATCH v2 net-next 4/5] net: fec: add change_mtu to support dynamic buffer allocation

Add a fec_change_mtu() handler to recalculate the pagepool_order based
on the new_mtu value. It will update the rx_frame_size accordingly if
the pagepool_order is changed.

If the interface is running, it stops RX/TX, and recreate the pagepool
with the new configuration.

Signed-off-by: Shenwei Wang <shenwei.wang@....com>
---
 drivers/net/ethernet/freescale/fec_main.c | 44 +++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 6d0d97bb077c..aa85a6d0b44f 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -4023,6 +4023,49 @@ static int fec_hwtstamp_set(struct net_device *ndev,
 	return fec_ptp_set(ndev, config, extack);
 }
 
+static int fec_change_mtu(struct net_device *ndev, int new_mtu)
+{
+	struct fec_enet_private *fep = netdev_priv(ndev);
+	int order, done;
+	bool running;
+
+	order = get_order(new_mtu + ETH_HLEN + ETH_FCS_LEN);
+	if (fep->pagepool_order == order) {
+		WRITE_ONCE(ndev->mtu, new_mtu);
+		return 0;
+	}
+
+	fep->pagepool_order = order;
+	fep->rx_frame_size = (PAGE_SIZE << order) - FEC_ENET_XDP_HEADROOM
+			     - SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+
+	running = netif_running(ndev);
+	if (!running) {
+		WRITE_ONCE(ndev->mtu, new_mtu);
+		return 0;
+	}
+
+	/* Stop TX/RX and free the buffers */
+	napi_disable(&fep->napi);
+	netif_tx_disable(ndev);
+	read_poll_timeout(fec_enet_rx_napi, done, (done == 0),
+			  10, 1000, false, &fep->napi, 10);
+	fec_stop(ndev);
+	fec_enet_free_buffers(ndev);
+
+	WRITE_ONCE(ndev->mtu, new_mtu);
+
+	/* Create the pagepool according the new mtu */
+	if (fec_enet_alloc_buffers(ndev) < 0)
+		return -ENOMEM;
+
+	fec_restart(ndev);
+	napi_enable(&fep->napi);
+	netif_tx_start_all_queues(ndev);
+
+	return 0;
+}
+
 static const struct net_device_ops fec_netdev_ops = {
 	.ndo_open		= fec_enet_open,
 	.ndo_stop		= fec_enet_close,
@@ -4032,6 +4075,7 @@ static const struct net_device_ops fec_netdev_ops = {
 	.ndo_validate_addr	= eth_validate_addr,
 	.ndo_tx_timeout		= fec_timeout,
 	.ndo_set_mac_address	= fec_set_mac_address,
+	.ndo_change_mtu		= fec_change_mtu,
 	.ndo_eth_ioctl		= phy_do_ioctl_running,
 	.ndo_set_features	= fec_set_features,
 	.ndo_bpf		= fec_enet_bpf,
-- 
2.43.0