linux-kernel - Re: [PATCH 1/2] arm64: dts: rockchip: correct uart mux for Radxa ZERO3

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Message-ID: <0DB47BC84E90B0E6+694b1274-4826-4ec1-9aa2-ca8aa790f61a@radxa.com>
Date: Fri, 19 Sep 2025 08:57:57 +0900
From: FUKAUMI Naoki <naoki@...xa.com>
To: Heiko Stübner <heiko@...ech.de>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org,
 linux-kernel@...r.kernel.org, Ed W <lists@...dgooses.com>
Subject: Re: [PATCH 1/2] arm64: dts: rockchip: correct uart mux for Radxa
 ZERO3

Hi Heiko, Ed,

On 9/19/25 01:18, Heiko Stübner wrote:
> Am Donnerstag, 18. September 2025, 17:23:04 Mitteleuropäische Sommerzeit schrieb Ed W:
>> On 18/09/2025 05:53, FUKAUMI Naoki wrote:
>>> Hi Ed,
>>>
>>> Thank you very much for your work.
>>>
>>> On 9/17/25 20:49, Ed Wildgoose wrote:
>>>> The rk3566 has multiplexed pins and the uarts can be moved to a choice
>>>> of 2 pin groups. The default rk356x-base.dtsi appears to default to mux0
>>>> for all uarts, however, specific hardware might choose to implement
>>>> alternatives
>>>>
>>>> The Radxa zero 3 shows that is uses M1 for uarts:
>>>> - uart4
>>>> - uart5
>>>> - uart9
>>>>
>>>> These aren't normally enabled, but we should at least correct the
>>>> default pinctrl definitions. Without these changes there will be
>>>> conflicts with mmc0/mmc1, leading to the SD or eMMC going missing.
>>>
>>> Sorry, but why do we need these definitions for disabled nodes?
>>>
>>> Or why don't we do similar definitions for nodes other than uart?
>>> For example, PWM12, I2S3, and SPI3 also use M1. Are they not related to SD/eMMC and therefore
>>> don't need to be defined?
>>>
>>> If users want to use UARTs on pin headers, they will refer to the correct documentation[1] to
>>> determine which pins are UARTs and will of course write the correct pinctrl definition.
>>>
>>> [1] https://docs.radxa.com/en/zero/zero3/hardware-design/hardware-interface#gpio-interface
>>>
>>> Best regards,
>>>
>>
>>
>> Personally, and I'm saying this as a user who is technical enough to fix the definitions, it took me
>> quite a few days to figure out what was wrong with the definitions and understand the intricate tree
>> of dtsi includes, to finally figure out why I couldn't just do a "status = "okay";" to enable the
>> UARTs... (which is roughly what is shown in several radxa supplied overlays to enable uarts on
>> various boards)
>>
>> So my vote would be to correctly define all the hardware for a given board. Then users can simply do
>> a status="okay" to enable and off they go.
> 
> And I'd agree with that argument. Setting up the needed pinctrl settings
> for the peripherals described in the device documentation
> ( https://docs.radxa.com/en/zero/zero3/hardware-design/hardware-interface#gpio-interface )
> 
> is the sensible thing to do. While keeping the peripherals itself disabled
> and for the user to decide which peripheral to enable.

I'm not strongly opposed to this policy, but I thought if you're going 
to do this, you should do it for everything, not just UARTs.

Best regards,

--
FUKAUMI Naoki
Radxa Computer (Shenzhen) Co., Ltd.

> Heiko
> 
> 
>