linux-kernel - Re: [PATCH 1/3] arm64: dts: rockchip: Change gmac phy-mode to rgmii-id for rk3576 evb1

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Message-ID: <d552639a-331e-436d-8baf-62546253aa62@rock-chips.com>
Date: Sat, 31 Jan 2026 14:26:05 +0800
From: Chaoyi Chen <chaoyi.chen@...k-chips.com>
To: Sebastian Reichel <sebastian.reichel@...labora.com>,
 Andrew Lunn <andrew@...n.ch>
Cc: Chaoyi Chen <kernel@...kyi.com>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Heiko Stuebner <heiko@...ech.de>,
 Alexey Charkov <alchark@...il.com>, Shawn Lin <shawn.lin@...k-chips.com>,
 Andy Yan <andy.yan@...k-chips.com>,
 Nicolas Frattaroli <nicolas.frattaroli@...labora.com>,
 Detlev Casanova <detlev.casanova@...labora.com>,
 Stephen Chen <stephen@...xa.com>, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] arm64: dts: rockchip: Change gmac phy-mode to
 rgmii-id for rk3576 evb1

On 1/22/2026 11:16 AM, Chaoyi Chen wrote:
> Hi Andrew,
> 
> On 1/22/2026 10:40 AM, Andrew Lunn wrote:
>> On Thu, Jan 22, 2026 at 09:38:17AM +0800, Chaoyi Chen wrote:
>>> Hi Andrew,
>>>
>>> On 1/21/2026 8:55 PM, Andrew Lunn wrote:
>>>>> @@ -721,6 +719,7 @@ rgmii_phy0: ethernet-phy@1 {
>>>>>  		reset-assert-us = <20000>;
>>>>>  		reset-deassert-us = <100000>;
>>>>>  		reset-gpios = <&gpio2 RK_PB5 GPIO_ACTIVE_LOW>;
>>>>> +		tx-internal-delay-ps = <1950>;
>>>>
>>>> The PHY should add 2000ps, as required by the RGMII standard. The
>>>> difference is so small there is no need for tx-internal-delay.
>>>>
>>>
>>> Thank you for the clarification. I chose 1950 here because I find that
>>> the MotorComm yt8xxx Ethernet PHY binding only offer the options of 
>>> 1950 or 2100. 
>>>
>>>> In most cases, 'rmgii-id' should be sufficient, unless the PCB is
>>>> badly designed.
>>>>
>>>
>>> I suspect the ROCK 4D board might be an exception. Sebastian once
>>> reported that it wouldn't work properly under "rgmii-id". Well, I'm
>>> not sure what strategy to adopt in this case.
>>
>> Please check the report. And also, check what the PHY is doing for
>> delays if you don't specify the property. Is it defaulting to near
>> 2000ps?
>>
> 
> It is RTL8211F PHY. The origin report is here:
> 
> https://lore.kernel.org/all/20250724-rk3576-rock4d-phy-timings-v1-1-1cdce2b4aca4@kernel.org/
> 
> The RTL8211F binding doesn't provide any indication of the default
> delay value. I'll checking datasheet to see if it's mentioned there.
> 

If "rgmii-id" is set, the RTL8211F driver adds the 2ns delay:

[0] https://elixir.bootlin.com/linux/v6.19-rc5/source/drivers/net/phy/realtek/realtek_main.c#L602

Sebastian, could you try testing how much extra delay the GMAC still
needs to add for the ROCK4D to work correctly, assuming the PHY
already has a 2 ns delay when "rgmii-id" is set?

-- 
Best, 
Chaoyi