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@nxp.com>
---
 drivers/net/ethernet/freescale/fec_main.c | 46 ++++++++++++++++++++++-
 1 file changed, 44 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 3f25db23d0de..aeeb2f81313c 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -470,14 +470,14 @@ 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 +4020,47 @@ 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;
+
+	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));
+
+	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);
+	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,
@@ -4029,6 +4070,7 @@ 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

> +static int fec_change_mtu(struct net_device *ndev, int new_mtu)
> +{
> +	struct fec_enet_private *fep = netdev_priv(ndev);
> +	int order, done;
> +
> +	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));
> +
> +	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);
> +	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;
> +

This is the wrong order. You need to first allocate the new buffers
and then free the old ones. If the allocation fails, you still have a
working interface using the smaller buffers, and the MTU change just
returns -ENOMEM. If you free the buffers and the allocation of the new
buffers fail, you interface is dead, because it has no buffers.

	Andrew