linux-kernel - Re: [PATCH v2 2/2] arm64: dts: rockchip: Add rk3576 evb2 board

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Message-ID: <CABjd4YxwD_q_FrEuPw_GY+vG6700Vd_weWqdcFn2C3V0fqpO-Q@mail.gmail.com>
Date: Thu, 8 Jan 2026 12:11:02 +0400
From: Alexey Charkov <alchark@...il.com>
To: Chaoyi Chen <kernel@...kyi.com>
Cc: Chaoyi Chen <chaoyi.chen@...k-chips.com>, Andrew Lunn <andrew@...n.ch>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Heiko Stuebner <heiko@...ech.de>, Quentin Schulz <quentin.schulz@...rry.de>, 
	Kever Yang <kever.yang@...k-chips.com>, Jonas Karlman <jonas@...boo.se>, 
	John Clark <inindev@...il.com>, FUKAUMI Naoki <naoki@...xa.com>, Jimmy Hon <honyuenkwun@...il.com>, 
	Dragan Simic <dsimic@...jaro.org>, Michael Riesch <michael.riesch@...labora.com>, 
	Peter Robinson <pbrobinson@...il.com>, Shawn Lin <shawn.lin@...k-chips.com>, 
	Sebastian Reichel <sebastian.reichel@...labora.com>, Andy Yan <andy.yan@...k-chips.com>, 
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] arm64: dts: rockchip: Add rk3576 evb2 board

On Thu, Jan 8, 2026 at 12:02 PM Chaoyi Chen <kernel@...kyi.com> wrote:
>
> On 1/8/2026 3:42 PM, Chaoyi Chen wrote:
> > Hello Alexey, Andrew,
> >
> > On 1/8/2026 2:53 PM, Alexey Charkov wrote:
> >> On Wed, Jan 7, 2026 at 10:18 PM Andrew Lunn <andrew@...n.ch> wrote:
> >>>
> >>>> +&gmac0 {
> >>>> +     clock_in_out = "output";
> >>>> +     phy-mode = "rgmii-rxid";
> >>>
> >>> rgmii-rxid is odd. Does the PCB really have an extra long TX clock
> >>> line, but a short RX clock line?
> >>>
> >>> Try changing this to rgmii-id, and drop the tx_delay property.
> >>
> >> Actually it would be great if Rockchip could clarify the delay
> >> duration introduced by a single delay element in GMAC-IOMUX delay
> >> lines, which are controlled in the GMAC driver by the {tx,rx}_delay
> >> properties. Maybe we could then switch to using
> >> {tx,rx}_internal_delay_ps for fine-tuning the delays on the GMAC side
> >> as envisaged in DT bindings [1], and use phy-mode = "rgmii-id"
> >> throughout. Chaoyi, any chance you could ask around in your hardware
> >> team?
> >>
> >> Currently though removing the delays at GMAC side altogether causes
> >> unstable link operation - see [2] for example.
> >>
> >> [1] https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/net/ethernet-controller.yaml#L342-L347
> >> [2] https://gitlab.collabora.com/hardware-enablement/rockchip-3588/linux/-/commit/372f3e9ae62cc62cdf2543391ea57be6bb548a0c
> >
> > Sorry, this problem has been discussed many times before. It's because
> > the gmac on the Rockchip platform currently relies on setting the
> > corresponding delay via phy-mode [3].
> >
> > [3] https://lore.kernel.org/all/mqoyjn7mnq6tmt6n6oev4wa3herjaxlupml2fmcampwiajvj4a@r5zs4d3jdm5p/
> >
> > The delay introduced by the delay line is not absolute. In reality,
> > it depends on factors such as the chip's design and process technology.
> >
> > And for RK3576, you can assume that:
> >
> >       time(ns) = 0.0579 * delay_line_count + 0.105
> >
> > For example, tx_delay = <0x20> means:
> >
> >       time = 0.0579 * 0x20 + 0.105 ns = 1.9578 ns
> >
> > And I believe {tx,rx}_internal_delay_ps is indeed a good idea.
> > I'll try to add them in v3. Thanks.
> >
>
> I've also see some dt that use {tx,rx}_internal_delay_ps inside the PHY,
> and compared to doing it in the MAC, which one is the better choice?

Your PHY defaults to 1950ps in rgmii-id [1], so adding anything on top
of that on GMAC side would land you with a longer total TX delay than
you currently get according to the coefficients you've just posted
(1784.1ps). I would say go for "tx-internal-delay-ps = <1800>" on the
PHY side for the closest match.

[1] https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/net/motorcomm%2Cyt8xxx.yaml#L36

Best regards,
Alexey