netdev - Re: [PATCH] dt-bindings: net: renesas,ethertsn: Add bindings for Ethernet TSN

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Date: Wed, 22 Nov 2023 14:57:06 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>,
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	devicetree@...r.kernel.org, netdev@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH] dt-bindings: net: renesas,ethertsn: Add bindings for
 Ethernet TSN

> > In general, we try to have the PHY add the delay, not the MAC. So i
> > would start with hard coding the delay to 0ns, and only implement
> > these properties if you have a board where the PHY cannot add the
> > delay.
> 
> If I understand the KSZ9031 bindings correctly, that PHY is limited to
> a skew of up to 960 ps, not 1800 or 2000 ps.

Reading ksz9031_config_rgmii_delay(), it implements the four
PHY_INTERFACE_MODE_RGMII* interface modes. So it should be able to
provide the 2ns delay. Sometimes the tuning ability is relative to the
base delay. So maybe it can do 2n +- 0.960/2 ?

Anyway, try interface mode "rgmii_id" with the MAC not providing any
delay.

	Andrew