RE: [PATCH 2/2] ARM: dts: imx6ull-dhcor: Add Marantec maveo box

[Christoph Niedermaier]

From: Marek Vasut [mailto:marex@xxxxxxx]
Sent: Thursday, April 6, 2023 4:10 PM
> On 4/6/23 10:37, Christoph Niedermaier wrote:
>> From: Marek Vasut [mailto:marex@xxxxxxx]
>> Sent: Wednesday, April 5, 2023 8:47 PM
>>> On 4/5/23 20:24, Christoph Niedermaier wrote:
>>>> From: Marek Vasut [mailto:marex@xxxxxxx]
>>>> 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.
>>>
>>> +CC Ulf , I vaguely recall some discussion about this enumeration and I
>>> am not sure one can really depend on that.
>>
>> That why I think it good to have a defined number for mmcblk devices
>> on an embedded system. An excerpt from [1]:
> 
> I might be misremembering this, but could it be that, if any non-OF
> SDMMC controller probes early and hogs the /dev/mmcblk2 before the OF
> ones have a chance to probe, then the OF ones would fail to probe ?
> 
>> Alternative solutions like PARTUUIDs do not cover the case where multiple
>> mmcblk devices contain the same image.
> 
> I agree, this is indeed a downside of PARTUUID .
> 
>> This is a common issue on devices
>> that can boot both from eMMC (for regular boot) and SD cards (as a
>> temporary boot medium for development). When a firmware image is
>> installed to eMMC after a test boot via SD card, there will be no
>> reliable way to refer to a specific device using (PART)UUIDs oder
>> LABELs
> 
> This can be solved by the installer updating the PARTUUID on the eMMC
> however.
> 
>> [1] https://patchwork.kernel.org/project/linux-mmc/patch/20200825134441.17537-2-matthias.schiffer@xxxxxxxxxxxxxxx/
>>
>> So far I have never had a problem with numbering mmcblk devices via aliases.
> 
> Based on the above, I don't think either the aliases or PARTUUID is a
> perfect solution, but the aliases should be fine for mx6ull at least?
> So I think we can conclude this discussion thread ?

Yes, I will send a new version with the changes on the first patch.

Regards
Christoph