linux-kernel - Re: [PATCH net-next 3/3] net: stmmac: Set CIC bit only for TX queues with COE

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Message-ID: <20250714134012.GN721198@horms.kernel.org>
Date: Mon, 14 Jul 2025 14:40:12 +0100
From: Simon Horman <horms@...nel.org>
To: rohan.g.thomas@...era.com
Cc: 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>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Serge Semin <fancer.lancer@...il.com>,
	Romain Gantois <romain.gantois@...tlin.com>, netdev@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Matthew Gerlach <matthew.gerlach@...era.com>
Subject: Re: [PATCH net-next 3/3] net: stmmac: Set CIC bit only for TX queues
 with COE

On Mon, Jul 14, 2025 at 03:59:19PM +0800, Rohan G Thomas via B4 Relay wrote:
> From: Rohan G Thomas <rohan.g.thomas@...era.com>
> 
> Currently, in the AF_XDP transmit paths, the CIC bit of
> TX Desc3 is set for all packets. Setting this bit for
> packets transmitting through queues that don't support
> checksum offloading causes the TX DMA to get stuck after
> transmitting some packets. This patch ensures the CIC bit
> of TX Desc3 is set only if the TX queue supports checksum
> offloading.
> 
> Signed-off-by: Rohan G Thomas <rohan.g.thomas@...era.com>
> Reviewed-by: Matthew Gerlach <matthew.gerlach@...era.com>

Hi Rohan,

I notice that stmmac_xmit() handles a few other cases where
checksum offload should not be requested via stmmac_prepare_tx_desc:

        csum_insertion = (skb->ip_summed == CHECKSUM_PARTIAL);
        /* DWMAC IPs can be synthesized to support tx coe only for a few tx
         * queues. In that case, checksum offloading for those queues that don't
         * support tx coe needs to fallback to software checksum calculation.
         *
         * Packets that won't trigger the COE e.g. most DSA-tagged packets will
         * also have to be checksummed in software.
         */
        if (csum_insertion &&
            (priv->plat->tx_queues_cfg[queue].coe_unsupported ||
             !stmmac_has_ip_ethertype(skb))) {
                if (unlikely(skb_checksum_help(skb)))
                        goto dma_map_err;
                csum_insertion = !csum_insertion;
        }

Do we need to care about them in stmmac_xdp_xmit_zc()
and stmmac_xdp_xmit_xdpf() too?

...