Re: [PATCH 11/12] riscv: dts: ultrarisc: Add Shenzhen Rongda M0 board device tree

On 2026-08-27 04:46 +0200, Andrew Lunn wrote:
> On Thu, Aug 27, 2026 at 10:19:43AM +0800, Jia Wang wrote:
> > On 2026-08-24 15:02 +0200, Andrew Lunn wrote:
> > > > +&ethernet {
> > > > +	phy-handle = <&phy0>;
> > > > +	/*
> > > > +	 * YT8531 RGMII timing on this board requires no PHY internal delays.
> > > 
> > > Please extend this sentence with an explanation why it needs no delay?
> > > 
> > > There are times this is correct, but it is also mostly wrong. Without
> > > an explanation, i cannot say if this is correct or not.
> > > 
> > 
> > Thanks for the review.
> > 
> > The DP1000 SoC integration provides the required TX and RX RGMII clock
> > skew, so enabling the YT8531 internal delays would apply the delay twice.
> 
> Please take a read of
> 
> https://elixir.bootlin.com/linux/v6.15/source/Documentation/devicetree/bindings/net/ethernet-controller.yaml#L287
> 
> You need to make the MAC driver do the correct thing:
> 
> # There are a small number of cases where the MAC has hard coded
> # delays which cannot be disabled. The 'phy-mode' only describes the
> # PCB.  The inability to disable the delays in the MAC does not change
> # the meaning of 'phy-mode'. It does however mean that a 'phy-mode' of
> # 'rgmii' is now invalid, it cannot be supported, since both the PCB
> # and the MAC and PHY adding delays cannot result in a functional
> # link. Thus the MAC should report a fatal error for any modes which
> # cannot be supported. When the MAC implements the delay, it must
> # ensure that the PHY does not also implement the same delay. So it
> # must modify the phy-mode it passes to the PHY, removing the delay it
> # has added. Failure to remove the delay will result in a
> # non-functioning link.
> 

Thanks for the clarification.

I will update the DTS to use "rgmii-id" and add a small DP1000 stmmac
glue driver. The driver will account for the fixed TX and RX MAC delays
using phy_fix_phy_mode_for_mac_delays(), reject unsupported modes, and
pass "rgmii" to the PHY.

>     Andrew
> 

Best regards,
Jia Wang



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