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

[Geert Uytterhoeven <geert@linux-m68k.org>]

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.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds