linux-kernel - Re: [PATCH net-next 1/4] dt-bindings: net: dsa: microchip: add SGMII port support to KSZ9477 switch

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Message-ID: <4d4d06e9-c0b4-4b49-a892-11efd07faf9a@lunn.ch>
Date: Thu, 15 Aug 2024 00:40:33 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Tristram.Ha@...rochip.com
Cc: Woojung.Huh@...rochip.com, UNGLinuxDriver@...rochip.com,
	devicetree@...r.kernel.org, f.fainelli@...il.com, olteanv@...il.com,
	robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, marex@...x.de, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 1/4] dt-bindings: net: dsa: microchip: add SGMII
 port support to KSZ9477 switch

> > The board should be designed such that the I2C bus pins of the SFP
> > cage are connected to an I2C controller. There are also a few pins
> > which ideally should be connected to GPIOs, LOS, Tx disable etc. You
> > can then put a node in DT describing the SFP cage:
> > 
> > Documentation/devicetree/bindings/net/sff,sfp.yaml
> > 
> >     sfp2: sfp {
> >       compatible = "sff,sfp";
> >       i2c-bus = <&sfp_i2c>;
> >       los-gpios = <&cps_gpio1 28 GPIO_ACTIVE_HIGH>;
> >       mod-def0-gpios = <&cps_gpio1 27 GPIO_ACTIVE_LOW>;
> >       pinctrl-names = "default";
> >       pinctrl-0 = <&cps_sfpp0_pins>;
> >       tx-disable-gpios = <&cps_gpio1 29 GPIO_ACTIVE_HIGH>;
> >       tx-fault-gpios = <&cps_gpio1 26 GPIO_ACTIVE_HIGH>;
> >     };
> > 
> > and then the ethernet node has a link to it:
> > 
> >     ethernet {
> >       phy-names = "comphy";
> >       phys = <&cps_comphy5 0>;
> >       sfp = <&sfp1>;
> >     };
> > 
> > Phylink will then driver the SFP and tell the MAC what to do.
> 
> I do not think the KSZ9477 switch design allows I2C access to the SFP
> EEPROM.

This is not a switch design issue, it is a board design issue. Plenty
of Marvell switches have a PCR which do SGMII and 1000BaseX. Only the
SFP SERDES data lines are connected to the switch. The I2C bus and
other lines are connected to the SoC, not the switch.

Do you have the schematics for the board you are testing on? Is it
open? Can you give us a link?

	Andrew