netdev - Re: [PATCH v3 6/9] riscv: dts: starfive: visionfive-v1: Setup ethernet phy

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Date: Mon, 18 Dec 2023 13:43:52 +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>,
 Hal Feng <hal.feng@...rfivetech.com>,
 Michael Turquette <mturquette@...libre.com>, Stephen Boyd
 <sboyd@...nel.org>, 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-clk@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, kernel@...labora.com,
 Emil Renner Berthing <emil.renner.berthing@...onical.com>
Subject: Re: [PATCH v3 6/9] riscv: dts: starfive: visionfive-v1: Setup
 ethernet phy

On 12/17/23 19:55, Andrew Lunn wrote:
> On Fri, Dec 15, 2023 at 10:40:45PM +0200, Cristian Ciocaltea wrote:
>> The StarFive VisionFive V1 SBC uses 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.
>>
>> Also note this adjustment is not necessary on BeagleV Starlight SBC,
>> which uses a Microchip PHY.  Hence, there is no indication of a
>> miss-behaviour on the GMAC side, but most likely the issue stems from
>> the Motorcomm PHY.
> 
> I suggest you make a similar comment in the .dts file, just to explain
> the odd setting.

Sure, will do, we need a v4 anyway.

Thanks,
Cristian