linux-kernel - Re: [PATCH v2 11/12] riscv: dts: starfive: visionfive-v1: Enable gmac and setup phy

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Date:   Mon, 30 Oct 2023 01:35:14 +0200
From:   Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Emil Renner Berthing <kernel@...il.dk>,
        Samin Guo <samin.guo@...rfivetech.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Richard Cochran <richardcochran@...il.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...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 v2 11/12] riscv: dts: starfive: visionfive-v1: Enable gmac
 and setup phy

On 10/30/23 00:50, Andrew Lunn wrote:
> On Mon, Oct 30, 2023 at 12:41:23AM +0200, Cristian Ciocaltea wrote:
>> On 10/29/23 20:45, Andrew Lunn wrote:
>>> On Sun, Oct 29, 2023 at 06:27:11AM +0200, Cristian Ciocaltea wrote:
>>>> The StarFive VisionFive V1 SBC has a Motorcomm YT8521 PHY supporting
>>>> RGMII-ID, but requires manual adjustment of the RX internal delay to
>>>> work properly.
>>>>
>>>> The default RX delay provided by the driver is 1.95 ns, which proves to
>>>> be too high. Applying a 50% reduction seems to mitigate the issue.
>>>
>>> I'm not so happy this cannot be explained. You are potentially heading
>>> into horrible backwards compatibility problems with old DT blobs and
>>> new kernels once this is explained and fixed.
>>
>> It seems the visionfive-v2 board also required setting some delays, but
>> unfortunately no details were provided:
>>
>> 0104340a67b1 ("riscv: dts: starfive: visionfive 2: Add configuration of
>> mac and phy")
> 
> That board also uses a YT8531 PHY. Its possible this is somehow to do
> with the PHY. Which is why testing with the Microchip PHY is
> important. That should answer the question is it a SoC or a PHY
> problem.

There is also YT8531S, which looks compatible with YT8521, but YT8531
seems to be a bit different. Regardless of what VisionFive v2 is using,
it would be indeed interesting to find out how the Microchip PHY behaves
in this context.

Regards,
Cristian