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

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Message-ID: <2325560.3ZeAukHxDK@diego>
Date: Thu, 18 Sep 2025 18:18:22 +0200
From: Heiko Stübner <heiko@...ech.de>
To: FUKAUMI Naoki <naoki@...xa.com>, 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

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.

Heiko