linux-kernel - Re: [PATCH 2/5] ARM: dts: rockchip: assign a fixed index to mmc devices on rv1108 boards

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Message-ID: <CAK8P3a25iYksubCnQb1-e5yj=crEsK37RB9Hn4ZGZMwcVVrG7g@mail.gmail.com>
Date:   Wed, 10 Feb 2021 11:34:41 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Heiko Stübner <heiko@...ech.de>
Cc:     Johan Jonker <jbx6244@...il.com>, Rob Herring <robh+dt@...nel.org>,
        "open list:ARM/Rockchip SoC support" 
        <linux-rockchip@...ts.infradead.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 2/5] ARM: dts: rockchip: assign a fixed index to mmc
 devices on rv1108 boards

On Wed, Feb 10, 2021 at 12:50 AM Heiko Stübner <heiko@...ech.de> wrote:
> Am Dienstag, 9. Februar 2021, 23:25:40 CET schrieb Arnd Bergmann:
>
> Hmm, right now I don't see the disadvantage of missing mmc numbers.

It's inconsistent with the normal use of these aliases across other
platforms.

> As similarly we count i2c and serial numbers for a long time, even though
> not all of them appear on every board.

Yes, that is a similar mistake.

> Especially as the main goal is to simply have stable numbers and
> not having the mmc devices swap numbers on every boot.
>
> So right now we're not using them from a userspace POV but
> instead agreed on following the address ordering of the soc.
> so when ordering mmc controllers by their io-address, mmc0
> is the first one, then mmc1, etc.
>
> So just for my understanding, what is different for mmc?
> I guess to guarantee ongoing numbering similar to sd{a,b,c,...}
> Or should all aliases be duplicted in each board dts and not
> live in any soc dtsi?

Each board should have its own aliases node that describes
exactly which of the devices are wired up on that board, and
in which order. If there are connectors on the board that
are labeled in some form, then the aliases are meant to
match what is written on the board or in its documentation.

      Arnd