linux-kernel - Re: [PATCH 2/2] ARM: dts: imx6ull-dhcor: Add Marantec maveo box

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Date:   Thu, 6 Apr 2023 19:32:50 +0200
From:   Marek Vasut <marex@...x.de>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Christoph Niedermaier <cniedermaier@...electronics.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Fabio Estevam <festevam@...x.de>,
        NXP Linux Team <linux-imx@....com>,
        kernel <kernel@...electronics.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] ARM: dts: imx6ull-dhcor: Add Marantec maveo box

On 4/6/23 18:36, Krzysztof Kozlowski wrote:
> On 05/04/2023 20:24, Christoph Niedermaier wrote:
>> From: Marek Vasut [mailto:marex@...x.de]
>> Sent: Wednesday, April 5, 2023 6:25 PM
>>> On 4/5/23 18:02, Christoph Niedermaier wrote:
>>>
>>> [...]
>>>
>>>> +/ {
>>>> +     model = "DH electronics i.MX6ULL DHCOR on maveo box";
>>>> +     compatible = "dh,imx6ull-dhcor-maveo-box", "dh,imx6ull-dhcor-som",
>>>> +                  "fsl,imx6ull";
>>>> +
>>>> +     aliases {
>>>> +             /delete-property/ mmc0; /* Avoid double definitions */
>>>> +             /delete-property/ mmc1;
>>>> +             mmc2 = &usdhc2; /* eMMC should be mmc2 */
>>>
>>> Why not mmc0 ?
>>>
>>> Use root=PARTUUID= when booting to avoid any dependency on
>>> root=/dev/mmcblk2pN enumeration.
>>
>> This is due to software interchangeability with the DHCOM
>> i.MX6ULL, where the eMMC is always mmc2.
> 
> That's not the reason to have aliases. The number should match numbering
> in your datasheet/schematics/user-guide, not what your software wants.
> 
> Use PARTUUID for SW dependencies.

Regarding the PARTUUID, Christoph raised a valid concern I think. These 
machines can come with A/B update scheme, where the PARTUUID could 
become identical between two partitions. Or, you can write the same 
image to both eMMC and SD card. I don't think PARTUUID is the silver 
bullet solution, but I agree the enumeration is a great solution either.