netdev - Re: [PATCH net 0/1] Prevent DSA tags from breaking COE

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Date: Fri, 22 Dec 2023 14:08:38 -0500
From: Household Cang <canghousehold@....com>
To: Vladimir Oltean <olteanv@...il.com>
Cc: Romain Gantois <romain.gantois@...tlin.com>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>,
 Jose Abreu <joabreu@...opsys.com>,
 "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>,
 Miquel Raynal <miquel.raynal@...tlin.com>,
 Maxime Chevallier <maxime.chevallier@...tlin.com>,
 Sylvain Girard <sylvain.girard@...com>,
 Pascal EBERHARD <pascal.eberhard@...com>,
 Richard Tresidder <rtresidd@...ctromag.com.au>,
 netdev@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH net 0/1] Prevent DSA tags from breaking COE

> On Dec 22, 2023, at 7:30 AM, Vladimir Oltean <olteanv@...il.com> wrote:
> 
> Is "rx off" actually required, or just "tx off”?

Before adjusted the ethtool -K, the client upload speed is 880Mbps (download speed 0.6Mbps). RK3568 is acting as a router, so client is sending to eth1 via DSA user port, rx used here, and then tx on eth0. So this might suggest only tx needs to be turned off on eth1.

> 
> The MT7531BE switch requires transmitted packets to have an additional
> header which indicates what switch port is targeted. So the packet
> structure is not the same as what eth0 transmits.
> 

I understand. How many bytes are the DSA header for MT, 8 bytes?

> Your GMAC datasheet should explain what packets it is able to offload
> L4 checksumming for, quite plainly. Probably MAC + IP + TCP yes, but
> MAC + MTK DSA + IP + TCP no.

I hardly could find this in the data sheet for RK3568. From the DMA mapping, it insinuates a correct ether type needs to be detected after the MAC header, besides an inner and an outer VLAN tag, if there are any.

>  The driver still declares
> the NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM features because it is able to
> offload checksumming for _some_ packets, but it falls back to the
> software checksum helper for the rest. This includes your MTK DSA tagged
> packets.

I guess the end verdict regarding whether the hardware supports checksum offloading on DSA frames is a NO. So this is going to use some precious CPU power I am looking to fully dedicate to ipsec. Though I am pursuing crypto hw offloading at the same time with baylibre.

Lucas.