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: <feb15456-2a16-4323-9d69-16aa842603f2@altera.com>
Date: Thu, 21 Aug 2025 19:20:02 +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 8/20/2025 9:26 PM, Jakub Kicinski wrote:
> On Wed, 20 Aug 2025 08:54:46 -0700 Jakub Kicinski wrote:
>> On Wed, 20 Aug 2025 12:44:18 +0530 G Thomas, Rohan wrote:
>>> On 8/20/2025 6:52 AM, Jakub Kicinski wrote:
>>>> Hopefully the slight pointer chasing here doesn't impact performance?
>>>> XDP itself doesn't support checksum so perhaps we could always pass
>>>> false?
>>>
>>> I'm not certain whether some XDP applications might be benefiting from
>>> checksum offloading currently
>>
>> Checksum offload is not supported in real XDP, AFAIK, and in AF_XDP
>> the driver must implement a checksum callback which stmmac does not do.
>> IOW it's not possible to use Tx checksum offload in stmmac today from
>> XDP.
> 
> To be clear -- this is just for context. I don't understand the details
> of what the CIC bit controls, so the final decision is up to you.

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.

Best Regards,
Rohan