linux-kernel - Re: [PATCH] ARM: dts: sunxi: Add MMC alias for consistent enumeration

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Message-ID: <d4cafa3f-d17c-4f80-bb30-98c28ede1077@stefan-gloor.ch>
Date: Sun, 5 Jan 2025 13:47:55 +0100
From: Stefan Gloor <code@...fan-gloor.ch>
To: Andre Przywara <andre.przywara@....com>, Chen-Yu Tsai <wens@...e.org>
Cc: robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
 jernej.skrabec@...il.com, samuel@...lland.org, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: dts: sunxi: Add MMC alias for consistent enumeration

Hi Chen-Yu and Andre, thank you for your input.

On 01.01.25 09:58, Chen-Yu Tsai wrote:

> IIRC we have chosen against adding explicit MMC aliases for the sunxi
> platforms. Please try using UUID= or PARTUUID= for root partition
> references.

I see, no problem. Out of curiosity, what is the reason for this 
decision? I couldn't find related discussions on the mailing list.

Personally, I like the UUID= or PARTUUID= method and I do have a working 
Yocto setup that uses PARTUUID to find the rootfs. It integrates nicely 
with the automatic disk/uuid creation and U-boot using extlinux.conf 
[1]. I do however understand that this requires major changes to the 
meta-sunxi layer and the maintainers don't like breaking a working 
system with U-boot scripts. So I went with the easier way of adding 
aliases. For future reference to anyone, this patch has now been added 
downstream to meta-sunxi [2].

[1] https://github.com/linux-sunxi/meta-sunxi/pull/431

[2] https://github.com/linux-sunxi/meta-sunxi/pull/432

On 02.01.25 00:28, Andre Przywara wrote:
> Yes, and LABEL= would be another way.
>
> Alternatively you could use U-Boot's DT when booting the board. U-Boot
> will add those aliases during build time (because it needs them for its
> own purposes), and by using $fdtcontroladdr (instead of $fdt_addr_r,
> on the bootz command line) you get this for free, and even save yourself
> from loading some DT.
> We sync the DTs regularly from the kernel to U-Boot now, and at the
> moment they are identical between the kernel and U-Boot, so you don't
> lose anything.

Thanks Andre for the helpful tips. I'll remember this for future reference.

Best,

Stefan