linux-kernel - Re: [PATCH 0/3] Support tuning the RX sampling swap of the MAC.

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Message-ID: <6dcfdb0b-c1ec-49f7-927e-531b20264d68@lunn.ch>
Date: Wed, 25 Dec 2024 18:49:07 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Yijie Yang <quic_yijiyang@...cinc.com>
Cc: Vinod Koul <vkoul@...nel.org>, Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Jose Abreu <joabreu@...opsys.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>, netdev@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 0/3] Support tuning the RX sampling swap of the MAC.

On Wed, Dec 25, 2024 at 06:04:44PM +0800, Yijie Yang wrote:
> The Ethernet MAC requires precise sampling times at Rx, but signals on the
> Rx side after transmission on the board may vary due to different hardware
> layouts. The RGMII_CONFIG2_RX_PROG_SWAP can be used to switch the sampling
> occasion between the rising edge and falling edge of the clock to meet the
> sampling requirements.

The RGMII specification says that RD[3:0] pins are sampled on the
rising edge for bits 3:0 and falling edge for bits 7:4.

Given this is part of the standard, why would you want to do anything
else?

Is this maybe another symptom of having the RGMII delays messed up?

Anyway, i don't see a need for this property, unless you are working
with a PHY which breaks the RGMII standard, and has its clock
reversed?

	Andrew