Re: [PATCH 1/1] arm64: dts: meson: g12b: odroid-n2: Assign a fixed index to mmc devices

From: Alexander Stein <alexander.stein@mailbox.org>
To: Rob Herring <robh+dt@kernel.org>,
	Kevin Hilman <khilman@baylibre.com>,
	Jerome Brunet <jbrunet@baylibre.com>,
	Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
	Neil Armstrong <narmstrong@baylibre.com>
Cc: devicetree@vger.kernel.org, linux-amlogic@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/1] arm64: dts: meson: g12b: odroid-n2: Assign a fixed index to mmc devices
Date: Fri, 29 Jan 2021 21:51:01 +0100	[thread overview]
Message-ID: <1975982.ltkoRUPMKj@kongar> (raw)
In-Reply-To: <8de4d82e-b9a5-f809-ea67-5527f9fdde5f@baylibre.com>

Hi,

Am Freitag, 29. Januar 2021, 09:07:45 CET schrieb Neil Armstrong:
> On 28/01/2021 00:08, Alexander Stein wrote:
> > Recently introduced async probe on mmc devices can shuffle block IDs.
> > Pin them to fixed values to ease booting in environments where UUIDs
> > are not practical. Use newly introduced aliases for mmcblk devices from 
[1].
> > [1]
> > https://patchwork.kernel.org/patch/11747669/
> 
> I understand the goal, and this should be done for _all_ boards, not only 
the Odroid-N2.

I see. So there are 2 options:
1.
Set the mapping for all 3 sd_emmc_* in the top-most .dtsi
Upside: very easy patch
Downside: When sd_emmc_a is not enabled "mmc0" will never be available.
Might be confusing.

2.
Set mapping only for enabled sd_emmc_* in the .dts[i] where it is enabled
Upside: Clean setup, only enabled sd_emmc_* have an alias
Downside: Much verbose patch(set)

Any preferences here? I honestly tend to 1. But this might break boards where
sd_emmc_a is not enabled, because the root device _will_ change in that case.

Best regards,
Alexander