linux-kernel - Re: [PATCH net-next 1/9] dt-bindings: phy: rename transmit-amplitude.yaml to phy-common-props.yaml

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Message-ID: <20251126105120.c7jtuy7rvbu4pqnv@skbuf>
Date: Wed, 26 Nov 2025 12:51:20 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: Holger Brunck <holger.brunck@...achienergy.com>
Cc: Andrew Lunn <andrew@...n.ch>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-phy@...ts.infradead.org" <linux-phy@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
	Daniel Golle <daniel@...rotopia.org>,
	Horatiu Vultur <horatiu.vultur@...rochip.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	"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>, Vinod Koul <vkoul@...nel.org>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Eric Woudstra <ericwouds@...il.com>,
	Marek Beh√∫n <kabel@...nel.org>,
	Lee Jones <lee@...nel.org>,
	Patrice Chotard <patrice.chotard@...s.st.com>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>
Subject: Re: [PATCH net-next 1/9] dt-bindings: phy: rename
 transmit-amplitude.yaml to phy-common-props.yaml

On Wed, Nov 26, 2025 at 10:45:31AM +0000, Holger Brunck wrote:
> the Kirkwood based board in question was OOT. Due to the patch we were
> able to use the mainline driver without patching it to configure the value we
> wanted.
> 
> The DTS node looked like this:
> 
> &mdio {
>         status = "okay";
> 
>         switch@10 {
>                 compatible = "marvell,mv88e6085";
>                 #address-cells = <1>;
>                 #size-cells = <0>;
>                 reg = <0x10>;
>                 ports {
>                         #address-cells = <1>;
>                         #size-cells = <0>;
>                         port@4 {
>                                 reg = <4>;
>                                 label = "port4";
>                                 phy-connection-type = "sgmii";
>                                 tx-p2p-microvolt = <604000>;
>                                 fixed-link {
>                                         speed = <1000>;
>                                         full-duplex;
>                                 };
>                         };
> 	};
> };

Perhaps there is some bit I'm missing, but let me try and run the code
on your sample device tree.

mv88e6xxx_setup_port()
	if (chip->info->ops->serdes_set_tx_amplitude) {
		dp = dsa_to_port(ds, port);
		if (dp)
			phy_handle = of_parse_phandle(dp->dn, "phy-handle", 0);

		if (phy_handle && !of_property_read_u32(phy_handle,
							"tx-p2p-microvolt",
							&tx_amp))
			err = chip->info->ops->serdes_set_tx_amplitude(chip,
								port, tx_amp);
		if (phy_handle) {
			of_node_put(phy_handle);
			if (err)
				return err;
		}
	}

dp->dn is the "port@4" node.
phy_handle is NULL, because the "port@4" node has no "phy-handle" property.
of_property_read_u32(phy_handle, "tx-p2p-microvolt") does not run
so chip->info->ops->serdes_set_tx_amplitude() is never called

I'm unable to reconcile the placement of the "tx-p2p-microvolt" property
in the port OF node with the code that searches for it exclusively in
the network PHY node.