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

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

On 05/28/2018 11:36 AM, Simon Horman wrote:
> On Mon, May 28, 2018 at 10:54:57AM +0200, Geert Uytterhoeven wrote:
>> Hi Simon,
>>
>> On Mon, May 28, 2018 at 10:41 AM, Simon Horman <horms@verge.net.au> wrote:
>>> On Thu, May 24, 2018 at 04:52:59PM +0200, Marek Vasut wrote:
>>>> On 05/23/2018 08:25 AM, Geert Uytterhoeven wrote:
>>>>> 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.
>>>
>>> Could you respin with this change?
>>>
>>> I would also like to ask for another change, in light of recent
>>> feedback from Olof Johansson ("Re: [GIT PULL] Renesas ARM64 Based SoC DT
>>> Updates for v4.18").
>>>
>>> Please consolidate the dts patches into a single patch?
>>
>> I think it's better to keep them split, as each commit description mentions
>> what needs to be passed on the kernel command line for the corresponding
>> board.
>>
>> Combining it in a single patch makes it much harder to extract this information.
>> Unless you're fine with a list:
>>
>>    koelsch: ...
>>    wheat: mtdparts=spi0.0:256k@0(loader),4096k(user),-(flash)
> 
> Lets try a list.

Reposted with a list, twice :/

-- 
Best regards,
Marek Vasut