Re: [PATCH net-next 2/2] net: stmmac: disable TX checksum offload for jumbo frames on bugged cores

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

Hi Lorenzo,

On 10/12/26 17:24, Lorenzo Bianconi wrote:
> stmmac_xdp_xmit_xdpf() decides TX checksum insertion from the queue COE
> capability only:
> 
> 	csum = !priv->plat->tx_queues_cfg[queue].coe_unsupported;
> 
> and lets the enhanced descriptor set TX_CIC_FULL accordingly. On the
> bugged_jumbo cores (snps,dwmac-3.40a, snps,dwmac-3.610 and
> snps,dwmac-3.710) hardware checksum insertion is broken for jumbo
> frames; the skb path works around it by clearing NETIF_F_CSUM_MASK in
> stmmac_fix_features() when the MTU exceeds ETH_DATA_LEN, so skbs are
> never marked CHECKSUM_PARTIAL and no checksum is inserted. The XDP TX
> path bypasses that workaround, so once XDP is allowed at MTU >
> ETH_DATA_LEN, jumbo frames sent via XDP_TX or redirected into the
> device would leave the interface with a full checksum insertion enabled
> on those cores - exactly what the workaround is meant to avoid.
> 
> Disable checksum insertion for oversized frames on bugged_jumbo cores in
> the XDP TX path too.
> 
> Fixes: be8b38a722e6 ("net: stmmac: Add support for XDP_TX action")
> Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@oss.qualcomm.com>

Looks cleaner to me than the alternative patch from Jisheng :

https://lore.kernel.org/netdev/20260929121025.20821-1-jszhang@kernel.org/

It sure seems there're a lot of people interested in getting XDP/XSK
working properly on stmmac :)

Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>

Maxime

> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index ca61ab449e32..0e29c5d04714 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -5276,6 +5276,14 @@ static int stmmac_xdp_xmit_xdpf(struct stmmac_priv *priv, int queue,
>  		return STMMAC_XDP_CONSUMED;
>  	}
>  
> +	/* Disable TX checksum offload for jumbo frames on cores where
> +	 * checksum insertion is broken for oversized frames, matching the
> +	 * stmmac_fix_features() workaround used by the skb path.
> +	 */
> +	if (priv->plat->bugged_jumbo &&
> +	    xdp_get_frame_len(xdpf) > ETH_FRAME_LEN)
> +		csum = false;
> +
>  	while (true) {
>  		skb_frag_t *frag = i ? &sinfo->frags[i - 1] : NULL;
>  		int len = frag ? skb_frag_size(frag) : xdpf->len;
>