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

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Message-ID: <46301ba1-16d0-8d7e-712b-c52aef52c576@linaro.org>
Date:   Thu, 6 Apr 2023 20:03:37 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Marek Vasut <marex@...x.de>,
        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 06/04/2023 19:32, Marek Vasut wrote:
> 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.

If you remove other aliases it means it comes only with emmc, right? One
storage. Then any A/B means you have two partitions. Two partitions will
have different PARTUUID as partition number is there. You can also use
PARTLABEL=root_a (root_b). That's BTW easy way to switch between A/B
partitions.

Best regards,
Krzysztof