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: <20250822070018.35692c26@kernel.org>
Date: Fri, 22 Aug 2025 07:00:18 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: "G Thomas, Rohan" <rohan.g.thomas@...era.com>
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

On Fri, 22 Aug 2025 18:19:01 +0530 G Thomas, Rohan wrote:
> 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.

Agreed.