linux-kernel - Re: 回覆: [net-next 2/4] ARM: dts: ast2600-evb: add default RGMII delay

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Message-ID: <8c0195dd-50b3-4f30-a021-c5b77d39d895@lunn.ch>
Date: Tue, 18 Mar 2025 15:03:03 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Jacky Chou <jacky_chou@...eedtech.com>
Cc: "andrew+netdev@...n.ch" <andrew+netdev@...n.ch>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>,
	"pabeni@...hat.com" <pabeni@...hat.com>,
	"robh@...nel.org" <robh@...nel.org>,
	"krzk+dt@...nel.org" <krzk+dt@...nel.org>,
	"conor+dt@...nel.org" <conor+dt@...nel.org>,
	"joel@....id.au" <joel@....id.au>,
	"andrew@...econstruct.com.au" <andrew@...econstruct.com.au>,
	"ratbert@...aday-tech.com" <ratbert@...aday-tech.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
	BMC-SW <BMC-SW@...eedtech.com>
Subject: Re: 回覆: [net-next 2/4] ARM:
 dts: ast2600-evb: add default RGMII delay

On Tue, Mar 18, 2025 at 11:00:27AM +0000, Jacky Chou wrote:
> Hi Andrew,
> 
> Thank you for your reply.
> 
> > >  	phy-mode = "rgmii";
> > >  	phy-handle = <&ethphy2>;
> > >
> > > +	tx-internal-delay-ps = <8>;
> > > +	rx-internal-delay-ps = <4>;
> > > +
> > 
> > Ideally you want:
> > 
> > 	phy-mode = "rgmii-id";
> > 	tx-internal-delay-ps = <0>;
> > 	rx-internal-delay-ps = <0>;
> > 
> > Since 'rgmii-id' correctly describes the hardware.
> 
> I still confuse about ethernet-controller.yaml.
> It lists 'rgmi', 'rgmii-rxid', 'rgmii-txid' and 'rgmii-id'.

DT describes the board. Does the board add the 2ns delay via extra
long clock lines? If yes, use rgmii. If the MAC/PHY pair need to add
the 2ns delay, use rgmii-id.

If the MAC/PHY pair is adding the delay, the DT says nothing about how
they add the delay.

The general rule is the PHY adds the delay. If you look at
drivers/net/phy/*.c, every PHY that implements RGMII support both
PHY_INTERFACE_MODE_RGMII_ID and PHY_INTERFACE_MODE_RGMII. There is no
reason not to follow ever other MAC/PHY pair and have the PHY add the
delay. The MAC can then do fine tuning if needed, adding small delays.

	Andrew