linux-kernel - Re: [PATCH v2 2/2] arm64: dts: qcom: qcs615-ride: Enable ethernet node

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Message-ID: <441f37f5-3c33-4c62-b3fe-728b43669e29@quicinc.com>
Date: Mon, 9 Dec 2024 10:11:23 +0800
From: Yijie Yang <quic_yijiyang@...cinc.com>
To: Andrew Lunn <andrew@...n.ch>
CC: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Bjorn Andersson
	<andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring
	<robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
	<conor+dt@...nel.org>,
        Richard Cochran <richardcochran@...il.com>,
        <linux-arm-msm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] arm64: dts: qcom: qcs615-ride: Enable ethernet
 node



On 2024-11-29 23:29, Andrew Lunn wrote:
>> I was mistaken earlier; it is actually the EMAC that will introduce a time
>> skew by shifting the phase of the clock in 'rgmii' mode.
> 
> This is fine, but not the normal way we do this. The Linux preference
> is that the PHY adds the delays. There are a few exceptions, boards
> which have PHYs which cannot add delays. In that case the MAC adds the
> delays. But this is pretty unusual.

After testing, it has been observed that modes other than 'rgmii' do not 
function properly due to the current configuration sequence in the 
driver code.

> 
> If you decided you want to be unusual and have the MAC add the delays,
> it should not be hard coded. You need to look at phy-mode. Only add

Are you suggesting that 'rgmii' indicates the delay is introduced by the 
board rather than the EMAC? But according to the 
Documentation/devicetree/bindings/net/ethernet-controller.yaml, this 
mode explicitly states that 'RX and TX delays are added by the MAC when 
required'. That is indeed my preference.

> delays for rgmii-id. And you then need to mask the value passed to the
> PHY, pass PHY_INTERFACE_MODE_RGMII, not PHY_INTERFACE_MODE_RGMII_ID,
> so the PHY does not add delays as well.
> 
> 	Andrew

-- 
Best Regards,
Yijie