[PATCH v2] arm64: dts: rockchip: Adjust RGMII TXD/RXD delays for the Rock Pi E

[Andrew Lunn]

On Fri, Dec 12, 2025 at 10:02:24PM +0000, Adrian Kossmann wrote:
> Current RGMII TXD/RXD delay results in link instability
> under load, with throughput eventually dropping to zero.
> Adjust the RGMII TXD/RXD delay values for stable link
> under load and stable Gigabit throughput
> 
> Signed-off-by: Adrian Kossmann <adrian.kossmann at posteo.de>
> ---
> Changes in v2:
> - Changed the patch subject as the last one contained
>   incorrect changes
> - Drop incorrect PHY compatible string change from v1
> - Adjustments to RGMII RX/TX delay values
> - Link to v1: https://lore.kernel.org/linux-rockchip/20251209210658.458506-2-adrian.kossmann@posteo.de/
> 
>  arch/arm64/boot/dts/rockchip/rk3328-rock-pi-e.dts | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/rockchip/rk3328-rock-pi-e.dts b/arch/arm64/boot/dts/rockchip/rk3328-rock-pi-e.dts
> index a4bdd87d0729..29ff0b8b8f18 100644
> --- a/arch/arm64/boot/dts/rockchip/rk3328-rock-pi-e.dts
> +++ b/arch/arm64/boot/dts/rockchip/rk3328-rock-pi-e.dts
> @@ -153,8 +153,8 @@ &gmac2io {
>  	phy-supply = <&vcc_io>;
>  	pinctrl-names = "default";
>  	pinctrl-0 = <&rgmiim1_pins>;
> -	tx_delay = <0x26>;
> -	rx_delay = <0x11>;
> +	tx_delay = <0x1a>;
> +	rx_delay = <0x14>;
>  	status = "okay";

You cannot see it here, it appears before this context:

&gmac2io {
        assigned-clocks = <&cru SCLK_MAC2IO>, <&cru SCLK_MAC2IO_EXT>;
        assigned-clock-parents = <&gmac_clkin>, <&gmac_clkin>;
        clock_in_out = "input";
        phy-handle = <&rtl8211>;
        phy-mode = "rgmii";

rgmii means the PCB provides the delay. I doubt that is the
case. Please try changing this to rgmii-id, as recommended here:

https://elixir.bootlin.com/linux/v6.15/source/Documentation/devicetree/bindings/net/ethernet-controller.yaml#L287

and then try out different rx_delay and tx_delay values.

    Andrew