Re: [PATCH 6/9] ARM: dts: wheat: Drop MTD partitioning from DT

[Marek Vasut <marek.vasut@gmail.com>]

On 05/23/2018 08:25 AM, Geert Uytterhoeven wrote:
> Hi Marek,
> 
> On Wed, May 23, 2018 at 12:01 AM, Marek Vasut <marek.vasut@gmail.com> wrote:
>> On 05/22/2018 04:43 PM, Geert Uytterhoeven wrote:
>>> On Tue, May 22, 2018 at 2:02 PM, Marek Vasut <marek.vasut@gmail.com> wrote:
>>>> Drop the MTD partitioning from DT, since it does not describe HW
>>>> and to give way to a more flexible kernel command line partition
>>>> passing.
>>>>
>>>> To retain the original partitioning, assure you have enabled
>>>> CONFIG_MTD_CMDLINE_PARTS in your kernel config and add the
>>>> following to your kernel command line:
>>>>
>>>>   mtdparts=spi0.0:256k@0(loader),4096k(user),-(flash)
>>>
>>> I think the "@0" can be dropped, as it's optional?
>>> 4m?
>>
>> My take on this is that the loader is actually at offset 0x0 of the MTD
>> device and we explicitly state that in the mtdparts to anchor the first
>> partition within the MTD device and all the other partitions are at
>> offset +(sum of the sizes of all partitions listed before the current
>> one) relative to that first partition.
> 
> Where is this explicitly states for the first partition?
> 
>> Removing the @0 feels fragile at best and it seems to depend on the
>> current behavior of the code.
> 
> Better, it also depends on the documented behavior:
> 
> Documentation/admin-guide/kernel-parameters.txt refers to
> drivers/mtd/cmdlinepart.c, which states:
> 
>  * <offset>  := standard linux memsize
>  *              if omitted the part will immediately follow the previous part
>  *              or 0 if the first part
> 
> None of the examples listed there or under the MTD_CMDLINE_PARTS Kconfig
> help text, or in a defconfig bundled with the kernel, use @0 for the first
> partition.

I think this is exceptionally fragile and dangerous to depend on this,
but so be it.

-- 
Best regards,
Marek Vasut