linux-kernel - Re: [PATCH] arch: arm64: dts: apple: Remove stdout-path

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Message-Id: <877czb42wk.fsf@bloch.sibelius.xs4all.nl>
Date:   Thu, 01 Dec 2022 15:25:15 +0100
From:   Mark Kettenis <mark.kettenis@...all.nl>
To:     Akihiko Odaki <akihiko.odaki@...nix.com>
Cc:     linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, asahi@...ts.linux.dev,
        krzysztof.kozlowski+dt@...aro.org, robh+dt@...nel.org,
        alyssa@...enzweig.io, sven@...npeter.dev, marcan@...can.st,
        akihiko.odaki@...nix.com
Subject: Re: [PATCH] arch: arm64: dts: apple: Remove stdout-path

> From: Akihiko Odaki <akihiko.odaki@...nix.com>
> Date: Thu,  1 Dec 2022 19:36:51 +0900
> 
> u-boot overrides stdout-path so that it points to /chosen/framebuffer
> with some condition.
> > arm: apple: Point stdout-path to framebuffer when keyboard present
> >
> > Unless you have a spare Apple Silicon machine, getting access to
> > the serial port on Apple Silicon machines requires special
> > hardware. Given that most machines come with a built-in screen
> > the framebuffer is likely to be the most convenient output device
> > for most users. While U-Boot will output to both serial and
> > framebuffer, OSes might not. Therefore set stdout-path to point
> > at /chosen/framebuffer when a keyboard is connected to the machine.
> https://github.com/AsahiLinux/u-boot/commit/a609353e82fd757b7635d18ed6a0828fff657d59
> 
> Perhaps it made sense to specify serial0 as stdout-path when the
> framebuffer and keyboard support was inmature, but today it is
> preferrable to use /chosen/framebuffer instead of serial0 for the
> console in the most cases as the u-boot change states.
> 
> Remove stdout-path to allow the kernel to choose the appropriate
> console. For Linux, it will be VT, which will be eventually backed by
> the framebuffer, if it is enabled. Otherwise, it will fall back to the
> serial.

U-Boot still relies on serial being the default.  It will not touch
stdout-out when running under the m1n1 hypervisor for example.  The
m1n1 hypervisor emulates the serial port hardware and developers rely
on this quite heavily.  Also, U-boot will only switch to the
framebuffer if a keyboard is connected.  This is currently disabled in
the builds for Asahi Linux because the type-A USB ports are not
supported yet in U-Boot.  But the plan is to fix that eventually.

So as far as I am concerted NAK.

> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
> ---
>  arch/arm64/boot/dts/apple/t600x-j314-j316.dtsi | 2 --
>  arch/arm64/boot/dts/apple/t600x-j375.dtsi      | 2 --
>  arch/arm64/boot/dts/apple/t8103-jxxx.dtsi      | 2 --
>  arch/arm64/boot/dts/apple/t8112-jxxx.dtsi      | 2 --
>  4 files changed, 8 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/apple/t600x-j314-j316.dtsi b/arch/arm64/boot/dts/apple/t600x-j314-j316.dtsi
> index 5547f5e7ac5a..14b6bf234f82 100644
> --- a/arch/arm64/boot/dts/apple/t600x-j314-j316.dtsi
> +++ b/arch/arm64/boot/dts/apple/t600x-j314-j316.dtsi
> @@ -30,8 +30,6 @@ chosen {
>  		#size-cells = <2>;
>  		ranges;
>  
> -		stdout-path = "serial0";
> -
>  		framebuffer0: framebuffer@0 {
>  			compatible = "apple,simple-framebuffer", "simple-framebuffer";
>  			reg = <0 0 0 0>; /* To be filled by loader */
> diff --git a/arch/arm64/boot/dts/apple/t600x-j375.dtsi b/arch/arm64/boot/dts/apple/t600x-j375.dtsi
> index 7c207b1df949..22e96b436bf2 100644
> --- a/arch/arm64/boot/dts/apple/t600x-j375.dtsi
> +++ b/arch/arm64/boot/dts/apple/t600x-j375.dtsi
> @@ -28,8 +28,6 @@ chosen {
>  		#size-cells = <2>;
>  		ranges;
>  
> -		stdout-path = "serial0";
> -
>  		framebuffer0: framebuffer@0 {
>  			compatible = "apple,simple-framebuffer", "simple-framebuffer";
>  			reg = <0 0 0 0>; /* To be filled by loader */
> diff --git a/arch/arm64/boot/dts/apple/t8103-jxxx.dtsi b/arch/arm64/boot/dts/apple/t8103-jxxx.dtsi
> index 3c5da0e5a41d..d2483f618d44 100644
> --- a/arch/arm64/boot/dts/apple/t8103-jxxx.dtsi
> +++ b/arch/arm64/boot/dts/apple/t8103-jxxx.dtsi
> @@ -27,8 +27,6 @@ chosen {
>  		#size-cells = <2>;
>  		ranges;
>  
> -		stdout-path = "serial0";
> -
>  		framebuffer0: framebuffer@0 {
>  			compatible = "apple,simple-framebuffer", "simple-framebuffer";
>  			reg = <0 0 0 0>; /* To be filled by loader */
> diff --git a/arch/arm64/boot/dts/apple/t8112-jxxx.dtsi b/arch/arm64/boot/dts/apple/t8112-jxxx.dtsi
> index b6b815d93c3e..af4153dcb55d 100644
> --- a/arch/arm64/boot/dts/apple/t8112-jxxx.dtsi
> +++ b/arch/arm64/boot/dts/apple/t8112-jxxx.dtsi
> @@ -22,8 +22,6 @@ chosen {
>  		#size-cells = <2>;
>  		ranges;
>  
> -		stdout-path = "serial0";
> -
>  		framebuffer0: framebuffer@0 {
>  			compatible = "apple,simple-framebuffer", "simple-framebuffer";
>  			reg = <0 0 0 0>; /* To be filled by loader */
> -- 
> 2.38.1
> 
> 
>