linux-kernel - Re: [PATCH] arm64: dts: rockchip: Change ethernet TXD timing delay value

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Message-ID: <aKU2yYD+N2D1KuHk@anyang>
Date: Wed, 20 Aug 2025 11:45:29 +0900
From: Dongjin Kim <tobetter@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Heiko Stuebner <heiko@...ech.de>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: rockchip: Change ethernet TXD timing delay
 value

On Tue, Aug 19, 2025 at 06:03:47PM +0200, Andrew Lunn wrote:
> On Tue, Aug 19, 2025 at 01:50:17PM +0900, Dongjin Kim wrote:
> > Very poor network performance is observed on the ODROID-M1 Board
> > (REV 1.0 20220613) when running iperf3 (under 200Mbits/sec), and
> > this problem can be resolved after changing the value of TXD
> > timing to 0x35 from 0x4f.
> 
> How did you decide on 0x35?
> 
> ~/linux/arch/arm64$ grep -hr "tx_delay = " | sort | uniq -c
>       4 	tx_delay = <0x10>;
>       1 	tx_delay = <0x1a>;
>       1 	tx_delay = <0x21>;
>       2 	tx_delay = <0x22>;
>       4 	tx_delay = <0x24>;
>       2 	tx_delay = <0x26>;
>      14 	tx_delay = <0x28>;
>       1 	tx_delay = <0x2a>;
>       6 	tx_delay = <0x30>;
>       1 	tx_delay = <0x3a>;
>       3 	tx_delay = <0x3c>;
>       2 	tx_delay = <0x42>;
>       5 	tx_delay = <0x43>;
>       2 	tx_delay = <0x44>;
>       1 	tx_delay = <0x46>;
>       6 	tx_delay = <0x4f>;
> 
> The numbers are all over the place, but it is clear that 0x28 is the
> most popular for some reason. But since this delay values are magic,
> i've no idea why.
> 
>      Andrew
I do have more numbers in the Rockchip BSP kernel, and 0x35 is from
one of them that shows less retry counts when testing 'iperf3' while
testing with the batch of ODROID-M1. :)

Thanks,
Dongjin Kim.