linux-kernel - Re: [PATCH v2 2/2] arm64: dts: freescale: Add SKOV IMX8MP CPU revB board

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Message-ID: <20231103125306.GB40819@pengutronix.de>
Date:   Fri, 3 Nov 2023 13:53:06 +0100
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     devicetree@...r.kernel.org, Fabio Estevam <festevam@...il.com>,
        kernel@...gutronix.de, Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        NXP Linux Team <linux-imx@....com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Søren Andersen <san@...v.dk>,
        Sam Ravnborg <sam@...nborg.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/2] arm64: dts: freescale: Add SKOV IMX8MP CPU revB
 board

Hi Andrew,

On Fri, Nov 03, 2023 at 01:35:46PM +0100, Andrew Lunn wrote:
> > +			port@2 {
> > +				reg = <2>;
> > +				label = "cpu";
> > +				ethernet = <&eqos>;
> > +				/* 2ns rgmii-rxid is implemented on PCB.
> > +				 * Switch should add only rgmii-txid.
> > +				 */
> 
> Its unusual to actually see that. Its even more unusual its only one
> clock line. Can you actually see it on the PCB?

Yes. I even made a delay calculation by measuring this trace on PCB,
just to make sure I see it correctly.

> > +				phy-mode = "rgmii-txid";
> > +				tx-internal-delay-ps = <2000>;
> 
> Is this actually needed? rgmii-txid should add 2ns delay. Since this
> apparently works, i'm assuming setting tx-internal-delay-ps to 2ns
> does nothing, otherwise you would have a 4ns delay.

Without it the driver will complain:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/dsa/microchip/ksz_common.c?h=v6.6#n3496

but it works as expected.

Regards,
Oleksij
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