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

From: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
To: Andrew Lunn <andrew@lunn.ch>
Cc: "David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Emil Renner Berthing <kernel@esmil.dk>,
	Samin Guo <samin.guo@starfivetech.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Torgue <alexandre.torgue@foss.st.com>,
	Jose Abreu <joabreu@synopsys.com>,
	Maxime Coquelin <mcoquelin.stm32@gmail.com>,
	Richard Cochran <richardcochran@gmail.com>,
	Giuseppe Cavallaro <peppe.cavallaro@st.com>,
	netdev@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
	linux-stm32@st-md-mailman.stormreply.com,
	linux-arm-kernel@lists.infradead.org, kernel@collabora.com
Subject: Re: [PATCH v2 11/12] riscv: dts: starfive: visionfive-v1: Enable gmac and setup phy
Date: Mon, 30 Oct 2023 01:35:14 +0200	[thread overview]
Message-ID: <7eab89f4-bfd0-441c-8b02-aa9d0f0cdace@collabora.com> (raw)
In-Reply-To: <e837e707-5b01-4b7b-8362-0dc62883fdba@lunn.ch>

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

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