[PATCH] riscv: dts: spacemit: k3-pico-itx: Fix non-functional ethernet TX timing

[Inochi Amaoto]

On Mon, Jun 08, 2026 at 08:23:58PM +0200, Andrew Rembrandt wrote:
> The "rgmii-id" PHY mode applies a symmetric 2ns internal delay in the
> PHY. On the Pico-ITX board this leaves insufficient TX timing margin and
> no ethernet traffic passes.
> 
> Add a 400ps MAC-side TX internal delay on top of the PHY's delay to
> correct the TX clock/data skew. The value follows the vendor fork's
> asymmetric tuning (tx-phase 73 x 33.3ps - 2000ps ID ~= 400ps); the
> driver rounds tx-internal-delay-ps to the nearest supported step.
> 
> This builds on commit 3ea695eb111f ("dts: riscv: spacemit: k3: Fix I/O
> power settings"), which fixed the GMAC0 1.8V/3.3V I/O switch
> 
> Tested on Pico-ITX hardware with iperf3: 60s TCP each direction and 60s
> UDP, all at 1Gbps with no TX/RX errors on the interface.
> 
> Fixes: 74657a376960 ("riscv: dts: spacemit: Add ethernet device for K3")
> Signed-off-by: Andrew Rembrandt <kernel at rembrandt.dev>
> ---
>  arch/riscv/boot/dts/spacemit/k3-pico-itx.dts | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/riscv/boot/dts/spacemit/k3-pico-itx.dts b/arch/riscv/boot/dts/spacemit/k3-pico-itx.dts
> index b89c1521e664..59aecaa2d32a 100644
> --- a/arch/riscv/boot/dts/spacemit/k3-pico-itx.dts
> +++ b/arch/riscv/boot/dts/spacemit/k3-pico-itx.dts
> @@ -186,6 +186,7 @@ &eth0 {
>  	pinctrl-names = "default";
>  	pinctrl-0 = <&gmac0_rgmii_0_cfg>, <&gmac0_phy_0_cfg>;
>  	phy-mode = "rgmii-id";
> +	tx-internal-delay-ps = <400>;
>  	phy-handle = <&phy0>;
>  	status = "okay";
>  

You should set tx-internal-delay-ps of the phy instead of
the controller. This is a phy in "rgmii-id" mode.

Regards,
Inochi