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

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Date:   Thu, 16 Feb 2023 17:51:37 +0200
From:   Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Lee Jones <lee@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Emil Renner Berthing <kernel@...il.dk>,
        Conor Dooley <conor@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Richard Cochran <richardcochran@...il.com>,
        Sagar Kadam <sagar.kadam@...ive.com>,
        Yanhong Wang <yanhong.wang@...rfivetech.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, kernel@...labora.com
Subject: Re: [PATCH 07/12] dt-bindings: net: Add StarFive JH7100 SoC

On 2/15/23 15:01, Andrew Lunn wrote:
> 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@...20000 {
>>>> +      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.

I gave "rgmii-id" a try and it's not usable, I get too many errors. So 
"rgmii" should be the right choice here.

Thanks,
Cristian

>      Andrew
>