netdev - Re: [PATCH v5 net-next 4/5] net: fec: add change_mtu to support dynamic buffer allocation

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Message-ID: <aLoGqxZYQYB4QyBH@lizhi-Precision-Tower-5810>
Date: Thu, 4 Sep 2025 17:37:47 -0400
From: Frank Li <Frank.li@....com>
To: Shenwei Wang <shenwei.wang@....com>
Cc: 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>,
	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: Re: [PATCH v5 net-next 4/5] net: fec: add change_mtu to support
 dynamic buffer allocation

On Thu, Sep 04, 2025 at 03:35:01PM -0500, Shenwei Wang wrote:
> 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.

Remove "It will".

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

If the interface is running, stop RX/TX and ...

>
> Signed-off-by: Shenwei Wang <shenwei.wang@....com>
> ---
>  drivers/net/ethernet/freescale/fec.h      |  5 +-
>  drivers/net/ethernet/freescale/fec_main.c | 57 ++++++++++++++++++++++-
>  2 files changed, 58 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/ethernet/freescale/fec.h b/drivers/net/ethernet/freescale/fec.h
> index f1032a11aa76..0127cfa5529f 100644
> --- a/drivers/net/ethernet/freescale/fec.h
> +++ b/drivers/net/ethernet/freescale/fec.h
> @@ -348,10 +348,11 @@ struct bufdesc_ex {
>   * the skbuffer directly.
>   */
>
...
>
> +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 to update MAX_FL based on the new_mtu
> +	 * and free/re-allocate the buffers if needs.
> +	 */
> +	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);

I think you need move fep->pagepool_order and fep->rx_frame_size to here.
incase update rx_frame_size impact running queue.

Frank
> +
> +	WRITE_ONCE(ndev->mtu, new_mtu);
> +
> +	if (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 +4081,7 @@ 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
>