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

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Date: Wed, 22 Nov 2023 16:41:37 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Andrew Lunn <andrew@...n.ch>
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

Hi Andrew,

On Wed, Nov 22, 2023 at 2:57 PM Andrew Lunn <andrew@...n.ch> wrote:
> > > 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 ?

Oh, I do remember the regressions when the KSZ9031 driver started
implementing that :-(  See commit a6f51f2efa742df0 ("ravb: Add support
for explicit internal clock delay configuration") and the commits it
links to.

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

That's more or less what we had before, cfr. commit 9b81018185965a30
("arm64: dts: renesas: rcar-gen3: Convert EtherAVB to explicit delay
handling")...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds