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

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Message-ID: <68f10ee1-d4c8-4498-88b0-90c26d606466@lunn.ch>
Date: Mon, 10 Nov 2025 16:35:13 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Jacky Chou <jacky_chou@...eedtech.com>
Cc: 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, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-aspeed@...ts.ozlabs.org, taoren@...a.com
Subject: Re: [PATCH net-next v4 4/4] net: ftgmac100: Add RGMII delay support
 for AST2600

> +	/* Add a warning to notify the existed dts based on AST2600. It is
> +	 * recommended to update the dts to add the rx/tx-internal-delay-ps to
> +	 * specify the RGMII delay and we recommend using the "rgmii-id" for
> +	 * phy-mode property to tell the PHY enables TX/RX internal delay and
> +	 * add the corresponding rx/tx-internal-delay-ps properties.
> +	 */

I would not say that exactly. Normally you don't need
rx/tx-internal-delay-ps. It is only requires for badly designed boards
where the designer did not correctly balance the line lengths.  So i
would word this such that it is recommended to use "rgmii-id", and if
necessary, add small "rx/tx-internal-delay-ps" values.

> +	scu = syscon_regmap_lookup_by_phandle(np, "aspeed,scu");
> +	if (IS_ERR(scu)) {
> +		dev_err(dev, "failed to get aspeed,scu");
> +		return PTR_ERR(scu);
> +	}

This is an optional property. If it does not exist, you have an old DT
blob. It is not an error. So you need to do different things depending
on what the error code is. If it does not exist, just return 0 and
leave the hardware alone. If it is some other error report it, and
abort the probe.

> +
> +	ret = of_property_read_u32(np, "aspeed,rgmii-delay-ps",
> +				   &rgmii_delay_unit);
> +	if (ret) {
> +		dev_err(dev, "failed to get aspeed,rgmii-delay-ps value\n");
> +		return -EINVAL;
> +	}

Again, optional.

	Andrew