netdev - Re: [PATCH 3/3] arm64: dts: rockchip: Add RTL8367RB-VB switch to Radxa E24C

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Message-ID: <65023e38-0f90-4d12-8615-a595e399b516@kwiboo.se>
Date: Mon, 28 Jul 2025 16:57:50 +0200
From: Jonas Karlman <jonas@...boo.se>
To: Andrew Lunn <andrew@...n.ch>
Cc: Linus Walleij <linus.walleij@...aro.org>,
 Alvin Šipraga <alsi@...g-olufsen.dk>,
 Vladimir Oltean <olteanv@...il.com>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Heiko Stuebner <heiko@...ech.de>,
 "David S . Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Yao Zi <ziyao@...root.org>,
 Chukun Pan <amadeus@....edu.cn>, netdev@...r.kernel.org,
 linux-rockchip@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 3/3] arm64: dts: rockchip: Add RTL8367RB-VB switch to
 Radxa E24C

Hi Andrew,

On 7/27/2025 9:16 PM, Andrew Lunn wrote:
> On Sun, Jul 27, 2025 at 06:03:00PM +0000, Jonas Karlman wrote:
>> The Radxa E24C has a Realtek RTL8367RB-VB switch with four usable ports
>> and is connected using a fixed-link to GMAC1 on the RK3528 SoC.
>>
>> Add an ethernet-switch node to describe the RTL8367RB-VB switch.
>>
>> Signed-off-by: Jonas Karlman <jonas@...boo.se>
>> ---
>> Initial testing with iperf3 showed ~930-940 Mbits/sec in one direction
>> and only around ~1-2 Mbits/sec in the other direction.
>>
>> The RK3528 hardware design guide recommends that timing between TXCLK
>> and data is controlled by MAC, and timing between RXCLK and data is
>> controlled by PHY.
>>
>> Any mix of MAC (rx/tx delay) and switch (rx/tx internal delay) did not
>> seem to resolve this speed issue, however dropping snps,tso seems to fix
>> that issue.
> 
> It could well be that the Synopsis TSO code does not understand the
> DSA headers. When it takes a big block to TCP data and segments it,
> you need to have the DSA header on each segment. If it does not do
> that, only the first segment has the DSA header, the switch is going
> to be dropping all the other segments, causes TCP to do a lot of
> retries.

Thanks for your insights!

I can confirm that disable of TSO and RX checksum offload on the conduit
interface help fix any TCP speed issue and reduced UDP packet loss to a
minimum.

Regards,
Jonas

> 
>> Unsure what is best here, should MAC or switch add the delays?
> 
> It should not matter. 2ns is 2ns...
> 
> 	Andrew