netdev - [PATCH v4 net-next 4/5] net: fec: add change_mtu to support dynamic buffer allocation

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Message-ID: <20250831211557.190141-5-shenwei.wang@nxp.com>
Date: Sun, 31 Aug 2025 16:15:56 -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 v4 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 | 58 ++++++++++++++++++++++-
 1 file changed, 56 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index cf5118838f9c..43f342dd9099 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -233,6 +233,9 @@ MODULE_PARM_DESC(macaddr, "FEC Ethernet MAC address");
  * 2048 byte skbufs are allocated. However, alignment requirements
  * varies between FEC variants. Worst case is 64, so round down by 64.
  */
+#define FEC_DRV_RESERVE_SPACE \
+	(XDP_PACKET_HEADROOM + \
+	 SKB_DATA_ALIGN((unsigned int)sizeof(struct skb_shared_info)))
 #define PKT_MAXBUF_SIZE		(round_down(2048 - 64, 64))
 #define PKT_MINBUF_SIZE		64
 
@@ -470,14 +473,14 @@ fec_enet_create_page_pool(struct fec_enet_private *fep,
 {
 	struct bpf_prog *xdp_prog = READ_ONCE(fep->xdp_prog);
 	struct page_pool_params pp_params = {
-		.order = 0,
+		.order = fep->pagepool_order,
 		.flags = PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV,
 		.pool_size = size,
 		.nid = dev_to_node(&fep->pdev->dev),
 		.dev = &fep->pdev->dev,
 		.dma_dir = xdp_prog ? DMA_BIDIRECTIONAL : DMA_FROM_DEVICE,
 		.offset = FEC_ENET_XDP_HEADROOM,
-		.max_len = FEC_ENET_RX_FRSIZE,
+		.max_len = fep->rx_frame_size,
 	};
 	int err;
 
@@ -4020,6 +4023,56 @@ 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 old_mtu, old_order, old_size, order, done;
+	int ret = 0;
+
+	order = get_order(new_mtu + ETH_HLEN + ETH_FCS_LEN + FEC_DRV_RESERVE_SPACE);
+	old_order = fep->pagepool_order;
+	old_size = fep->rx_frame_size;
+	old_mtu = READ_ONCE(ndev->mtu);
+	fep->pagepool_order = order;
+	fep->rx_frame_size = (PAGE_SIZE << order) - FEC_DRV_RESERVE_SPACE;
+
+	if (!netif_running(ndev)) {
+		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);
+
+	WRITE_ONCE(ndev->mtu, new_mtu);
+
+	if (fep->pagepool_order != old_order) {
+		fec_enet_free_buffers(ndev);
+
+		/* Create the pagepool based on the new mtu.
+		 * Revert to the original settings if buffer
+		 * allocation fails.
+		 */
+		if (fec_enet_alloc_buffers(ndev) < 0) {
+			fep->pagepool_order = old_order;
+			fep->rx_frame_size = old_size;
+			WRITE_ONCE(ndev->mtu, old_mtu);
+			fec_enet_alloc_buffers(ndev);
+			ret = -ENOMEM;
+		}
+	}
+
+	fec_restart(ndev);
+	napi_enable(&fep->napi);
+	netif_tx_start_all_queues(ndev);
+
+	return ret;
+}
+
 static const struct net_device_ops fec_netdev_ops = {
 	.ndo_open		= fec_enet_open,
 	.ndo_stop		= fec_enet_close,
@@ -4029,6 +4082,7 @@ 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