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

[Inochi Amaoto]

On Tue, Jun 09, 2026 at 08:24:46PM +0200, Andrew Rembrandt wrote:
> On Tue, Jun 09, 2026 at 01:37:56 pm Inochi Amaoto wrote:
> > You should set tx-internal-delay-ps of the phy instead of
> > the controller. This is a phy in "rgmii-id" mode.
> Thanks for the review. I don't think that works on this board, but
> please let me know if I'm missing something.
> 
> The PHY is a Realtek RTL8211F. Its driver only toggles the chip's fixed
> ~2ns delay on/off from phy-mode, and per the datasheet that's a hardware
> limit, not a driver one -- the RTL8211F has no tunable delay, so a ps
> value on the PHY node has nothing to act on.
> 
> The only configurable delay element on K3 is the SoC RGMII delay line,
> and dwmac-spacemit programs it from tx-/rx-internal-delay-ps read off
> the controller node (spacemit_dwmac_probe()), so that is where the
> property has to live to take effect. This is the MAC "fine tuning ...
> values expected here are small" case described in
> Documentation/devicetree/bindings/net/ethernet-controller.yaml: the
> RTL8211F supplies the fixed ~2ns via rgmii-id and the MAC adds a 400ps
> trim on top. Ideally the PHY would own the delay, but as Andrew Lunn
> noted reviewing dwmac-meson8b, that requires the PHY to implement a
> configurable delay, which not all do.
> 
> The already-merged k1-bananapi-f3 does the same thing: eth1 combines
> phy-mode = "rgmii-id" with tx-internal-delay-ps = <250> on the
> controller node (via the K1 EMAC rather than dwmac, but the same DT
> pattern).
> 
> Would you be OK keeping it on the controller given the above? 

Yes, it is good for me.


> For v2 I can add an explicit rx-internal-delay-ps = <0> to match 
> the other SpacemiT boards (k1-bananapi-f3 included) and spell this
> reasoning out in the commit message.
> 

Do not do this, just leave the rx-internal-delay-ps untouched.

For this patch

Reviewed-by: Inochi Amaoto <inochiama at gmail.com>

Regards,
Inochi.