linux-kernel - [PATCH net-next v4 4/4] net: ftgmac100: Add RGMII delay support for AST2600

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Message-ID:
 <SEYPR06MB51347C9924E32731478BBDAB9DD9A@SEYPR06MB5134.apcprd06.prod.outlook.com>
Date: Wed, 3 Dec 2025 05:30:01 +0000
From: Jacky Chou <jacky_chou@...eedtech.com>
To: Andrew Lunn <andrew@...n.ch>
CC: Tao Ren <rentao.bupt@...il.com>, 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>, Po-Yu Chuang <ratbert@...aday-tech.com>, Joel
 Stanley <joel@....id.au>, Andrew Jeffery <andrew@...econstruct.com.au>,
	"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>, "taoren@...a.com" <taoren@...a.com>
Subject: [PATCH net-next v4 4/4] net: ftgmac100: Add RGMII delay support for
 AST2600

> > I miss one condition is using fixed-link property.
> > In ftgmac100, there are RGMII, NC-SI and fixed-link property.
> > On RGMII, we have solution on dedicated PHY, but there is an issue on
> > fixed-link property.
> >
> > Example on dedicated PHY.
> > The driver can pass the "rgmii-id" to tell PHY driver to enable the
> > internal delay on PHY side. Therefore, we can force to disable RGMII delay on
> MAC side.
> > But there is not any driver when using fixed-link property, which
> > means no body can tell the outside device, like switch or MAC-to-MAC,
> > to enable the internal delay on them. Also mean the phy-mode in fixed-link
> case is not used.
> >
> > Therefore, could we ignore the RGMII delay on MAC side when the
> > ftgmac100 driver gets the fixed-link property? Just keep the original delay
> value?
> 
> MAC to MAC is one of the edge cases where phy-mode is not great. What is
> generally accepted it to use rx-internal-delay-ps and tx-internal-delay-ps with
> 2ns and a comment explaining it is a MAC to MAC link, with this MAC adding
> the delays.
> 
> I suggest you see how messy it is to implement this for 2600. If the code looks
> horrible, keep the bootloader delays. For 2700 you have a clean slate, you can
> implement all this correctly from the start.
> 

Thank you for your suggestion.
We will discuss internally how to implement for these cases and prepare in next
version.

Thanks,
Jacky