Re: [PATCH 07/12] dt-bindings: net: Add StarFive JH7100 SoC

[Andrew Lunn]

On Wed, Feb 15, 2023 at 02:34:23AM +0200, Cristian Ciocaltea wrote:
> On 2/11/23 18:01, Andrew Lunn wrote:
> > > +  starfive,gtxclk-dlychain:
> > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > +    description: GTX clock delay chain setting
> > 
> > Please could you add more details to this. Is this controlling the
> > RGMII delays? 0ns or 2ns?
> 
> This is what gets written to JH7100_SYSMAIN_REGISTER49 and it's currently
> set to 4 in patch 12/12. As already mentioned, I don't have the register
> information in the datasheet, but I'll update this as soon as we get some
> details.

I have seen what happens to this value, but i have no idea what it
actually means. And without knowing what it means, i cannot say if it
is being used correctly or not. And it could be related to the next
part of my comment...

> 
> > > +    gmac: ethernet@10020000 {
> > > +      compatible = "starfive,jh7100-dwmac", "snps,dwmac";
> > > +      reg = <0x0 0x10020000 0x0 0x10000>;
> > > +      clocks = <&clkgen JH7100_CLK_GMAC_ROOT_DIV>,
> > > +               <&clkgen JH7100_CLK_GMAC_AHB>,
> > > +               <&clkgen JH7100_CLK_GMAC_PTP_REF>,
> > > +               <&clkgen JH7100_CLK_GMAC_GTX>,
> > > +               <&clkgen JH7100_CLK_GMAC_TX_INV>;
> > > +      clock-names = "stmmaceth", "pclk", "ptp_ref", "gtxc", "tx";
> > > +      resets = <&rstgen JH7100_RSTN_GMAC_AHB>;
> > > +      reset-names = "ahb";
> > > +      interrupts = <6>, <7>;
> > > +      interrupt-names = "macirq", "eth_wake_irq";
> > > +      max-frame-size = <9000>;
> > > +      phy-mode = "rgmii-txid";
> > 
> > This is unusual. Does your board have a really long RX clock line to
> > insert the 2ns delay needed on the RX side?
> 
> Just tested with "rgmii" and didn't notice any issues. If I'm not missing
> anything, I'll do the change in the next revision.

rgmii-id is generally the value to be used. That indicates the board
needs 2ns delays adding by something, either the MAC or the PHY. And
then i always recommend the MAC driver does nothing, pass the value to
the PHY and let the PHY add the delays.

So try both rgmii and rgmii-id and do a lot of bi directional
transfers. Then look at the reported ethernet frame check sum error
counts, both local and the link peer. I would expect one setting gives
you lots of errors, and the other works much better.

    Andrew