linux-kernel - Re: [PATCH v5 net-next 5/5] net: fec: enable the Jumbo frame support for i.MX8QM

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Message-ID: <aLoHOfNTCtVEFj6q@lizhi-Precision-Tower-5810>
Date: Thu, 4 Sep 2025 17:40:09 -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 5/5] net: fec: enable the Jumbo frame support
 for i.MX8QM

On Thu, Sep 04, 2025 at 03:35:02PM -0500, Shenwei Wang wrote:
> Certain i.MX SoCs, such as i.MX8QM and i.MX8QXP, feature enhanced
> FEC hardware that supports Ethernet Jumbo frames with packet sizes
> up to 16K bytes.
>
> When Jumbo frames are supported, the TX FIFO may not be large enough
> to hold an entire frame. To handle this, the FIFO is configured to
> operate in cut-through mode when the frame size exceeds
> (PKT_MAXBUF_SIZE - ETH_HLEN - ETH_FCS_LEN), which allows transmission
> to begin once the FIFO reaches a certain threshold.
>
> Signed-off-by: Shenwei Wang <shenwei.wang@....com>
> ---
>  drivers/net/ethernet/freescale/fec.h      |  3 +++
>  drivers/net/ethernet/freescale/fec_main.c | 25 +++++++++++++++++++----
>  2 files changed, 24 insertions(+), 4 deletions(-)
>
...
>
>  	if (fep->bufdesc_ex)
> @@ -4614,7 +4626,12 @@ fec_probe(struct platform_device *pdev)
>
>  	fep->pagepool_order = 0;
>  	fep->rx_frame_size = FEC_ENET_RX_FRSIZE;
> -	fep->max_buf_size = PKT_MAXBUF_SIZE;
> +
> +	if (fep->quirks & FEC_QUIRK_JUMBO_FRAME)
> +		fep->max_buf_size = MAX_JUMBO_BUF_SIZE;

If only use once, needn't define macro.

Frank
> +	else
> +		fep->max_buf_size = PKT_MAXBUF_SIZE;
> +
>  	ndev->max_mtu = fep->max_buf_size - ETH_HLEN - ETH_FCS_LEN;
>
>  	ret = register_netdev(ndev);
> --
> 2.43.0
>