netdev - Re: [PATCH v4 2/6] net: stmmac: Inverse the phy-mode definition

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Message-ID: <f93d325f-2c04-49ab-ae92-b87ae88ab49d@lunn.ch>
Date: Thu, 21 Aug 2025 05:33:22 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Yijie Yang <yijie.yang@....qualcomm.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>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.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>, netdev@...r.kernel.org,
	linux-arm-msm@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, stable+noautosel@...nel.org
Subject: Re: [PATCH v4 2/6] net: stmmac: Inverse the phy-mode definition

On Thu, Aug 21, 2025 at 10:22:05AM +0800, Yijie Yang wrote:
> 
> 
> On 2025-08-20 00:20, Andrew Lunn wrote:
> > >   static int ethqos_rgmii_macro_init(struct qcom_ethqos *ethqos, int speed)
> > >   {
> > >   	struct device *dev = &ethqos->pdev->dev;
> > > -	int phase_shift;
> > > +	int phase_shift = 0;
> > >   	int loopback;
> > >   	/* Determine if the PHY adds a 2 ns TX delay or the MAC handles it */
> > > -	if (ethqos->phy_mode == PHY_INTERFACE_MODE_RGMII_ID ||
> > > -	    ethqos->phy_mode == PHY_INTERFACE_MODE_RGMII_TXID)
> > > -		phase_shift = 0;
> > > -	else
> > > +	if (ethqos->phy_mode == PHY_INTERFACE_MODE_RGMII_ID)
> > >   		phase_shift = RGMII_CONFIG2_TX_CLK_PHASE_SHIFT_EN;
> > 
> > Does this one setting control both RX and TX delays? The hardware
> > cannot support 2ns delay on TX, but 0ns on RX? Or 2ns on RX but 0ns on
> > TX?
> > 
> 
> This setting is only for Tx delay. Rx delays are taken care separately with
> DLL delays.

If this is only for Tx delays, why is it also not used for
PHY_INTERFACE_MODE_RGMII_TXID?

It is simpler to just let the PHY add the delays, the PHY drivers get
this right, are well tested, and just work. MAC drivers often get
delays wrong.

	Andrew