linux-kernel - Re: [v1] arm64: dts: freescale: imx93-var-som: update eqos support for MaxLinear PHY

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Message-ID: <CAK+owog69JktbsBhHZj7ULYXmH_bZ-CO8=QEMqBVc0mjp8jz6g@mail.gmail.com>
Date: Wed, 4 Jun 2025 15:08:09 +0200
From: Stefano Radaelli <stefano.radaelli21@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, 
	Pengutronix Kernel Team <kernel@...gutronix.de>, Fabio Estevam <festevam@...il.com>, imx@...ts.linux.dev, 
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [v1] arm64: dts: freescale: imx93-var-som: update eqos support
 for MaxLinear PHY

Hi Andrew,

To clarify more precisely: hw team told me that the required 2 ns
RGMII delays are
implemented directly in hardware inside the SOM itself, through passive delay
elements (filters) placed on the RX and TX lines. There is no reliance on PHY
strap settings or any kind of delay configuration via registers.

This means:
- The delays are fixed and cannot be changed via software.
- From the point of view of any carrier board, the interface is
already timing-compliant.

Given that, using phy-mode = "rgmii" in the DTS is intentional and
correct, since the
necessary internal delays are already guaranteed by the SOM hardware design.

Let me know if further clarification would be helpful, would it help if I add a
clarification about this in the commit message for v2?

Best regards,
Stefano

Il giorno mer 4 giu 2025 alle ore 14:01 Andrew Lunn <andrew@...n.ch> ha scritto:
>
>
> 61;8001;1cOn Wed, Jun 04, 2025 at 09:37:39AM +0200, Stefano Radaelli wrote:
> > Hi Andrew,
> >
> > I double-checked with our hardware team, and it turns out that all required
> > RGMII delays are already handled by the hardware on the SOM (trace
> > tuning + PHY config).
>
> What do you mean by PHY config?
>
> The four RGMII modes you can use with phy-mode are purely about the
> PCB. If you have the PHY strapped to add delays, what does not count
> for PCB, and if you are not careful, future software could reconfigure
> it.
>
>         Andrew