linux-kernel - Re: [PATCH net-next v2 3/3] net: stmmac: Set CIC bit only for TX queues with COE

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Message-ID: <0f391b0a-6e9d-4581-9f3a-48e67ea90b31@altera.com>
Date: Fri, 22 Aug 2025 18:19:01 +0530
From: "G Thomas, Rohan" <rohan.g.thomas@...era.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Rohan G Thomas via B4 Relay
 <devnull+rohan.g.thomas.altera.com@...nel.org>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 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>,
 Jose Abreu <Jose.Abreu@...opsys.com>,
 Ong Boon Leong <boon.leong.ong@...el.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 v2 3/3] net: stmmac: Set CIC bit only for TX
 queues with COE

Hi Jakub,

On 8/21/2025 7:47 PM, Jakub Kicinski wrote:
>> Currently, in the stmmac driver, even though tmo_request_checksum is not
>> implemented, checksum offloading is still effectively enabled for AF_XDP
>> frames, as CIC bit for tx desc are set, which implies checksum
>> calculation and insertion by hardware for IP packets. So, I'm thinking
>> it is better to keep it as false only for queues that do not support
>> COE.
> Oh, so the device parses the packet and inserts the checksum whether
> user asked for it or not? Damn, I guess it may indeed be too late
> to fix, but that certainly_not_ how AF_XDP is supposed to work.
> The frame should not be modified without user asking for it..

Yes, I also agreed. But since not sure, currently any XDP applications
are benefiting from hw checksum, I think it's more reasonable to keep
csum flag as false only for queues that do not support COE, while
maintaining current behavior for queues that do support it. Please let
me know if you think otherwise.

Best Regards,
Rohan