linux-kernel - Re: [PATCH] arm64: dts: ls1028a: make the eMMC and SD card controllers use fixed indices

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Message-ID: <e1926b2c2cccfe19f66562b50a686088@walle.cc>
Date:   Thu, 19 Nov 2020 17:08:39 +0100
From:   Michael Walle <michael@...le.cc>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ashish Kumar <Ashish.Kumar@....com>,
        Yangbo Lu <yangbo.lu@....com>
Subject: Re: [PATCH] arm64: dts: ls1028a: make the eMMC and SD card
 controllers use fixed indices

Hi Vladimir,

Am 2020-11-19 16:50, schrieb Vladimir Oltean:
> As the boot order in the kernel continues to change, sometimes it may
> happen that the eSDHC controller mmc@...0000 (the one for eMMC) gets
> probed before the one at mmc@...0000 (for external SD cards). The 
> effect
> is that the eMMC controller gets the /dev/mmcblk0 name, and the SD card
> gets /dev/mmcblk1.

Thanks for taking care.

> Since the introduction of this SoC, that has never happened in 
> practice,
> even though it was never guaranteed in theory. Setting
> "root=/dev/mmcblk0p2" in /proc/cmdline has always caused the kernel to
> use the second partition from the SD card as the rootfs.
> 
> Preserve that old behavior by adding some aliases which create naming
> consistency:
> - the SD card controller uses /dev/mmcblk0
> - the eMMC controller uses /dev/mmcblk1

Could you change this behaviour for the sl28 board(s)? I've always
found it counter-intuitive to have mmcblk1 being the eMMC on a board
which always have the eMMC populated. All our images uses UUIDs for
the "root=" parameter and, technically, the order wasn't specified yet.

So I'd like to have the eMMC as /dev/mmcblk0 and the SD card as
/dev/mmcblk1.

-michael