[PATCH 1/2] ubi: mount partitions specified in device tree

[Hauke Mehrtens]

On 06/24/2016 08:28 PM, Ezequiel Garcia wrote:
> On 18 June 2016 at 16:35, Hauke Mehrtens <hauke at hauke-m.de> wrote:
>> On 06/18/2016 09:30 PM, Richard Weinberger wrote:
>>> Am 18.06.2016 um 21:17 schrieb Hauke Mehrtens:
>>>> This makes it possible to open a ubi layer in device tree, this is
>>>> helpful when the rootfs is on a ubi layer. It loops though all mtd
>>>> partitions and mounts the partition which is compatible with
>>>> "ubi,volume". The same was only possible with kernel command line
>>>> arguments before.
>>>>
>>>> Signed-off-by: Hauke Mehrtens <hauke at hauke-m.de>
>>>> ---
>>>>  Documentation/devicetree/bindings/mtd/ubi.txt | 33 ++++++++++++++
>>>>  drivers/mtd/ubi/block.c                       | 63 +++++++++++++++++++++++++++
>>>>  2 files changed, 96 insertions(+)
>>>>  create mode 100644 Documentation/devicetree/bindings/mtd/ubi.txt
>>>
>>> Some time ago I thought about an UBI DT binding too, but
>>> I have been told that device tree is only for describing the hardware
>>> and nothing else.
>>> So I fear this will be rejected by DT folks.
>>
>> There are some devices on the market that are storing the root file
>> system in an ubi layer.
>> To make this work there are currently two options.
>> 1. patch the kernel to specify which partitions to open in the code.
> 
> I wouldn't go as far as to claim this an option.

I would also not do this, but when you look into the Linux patches of
"professional" embedded devices you see many strange things.

> 
>> 2. provide some kernel command line parameter which specifies what to open.
>>
> 
> There's another option: use an initramfs, where you can do whatever you want
> to find your UBI and mount it.

An initramfs probably needs some 10 to 100 KBytes of additional memory
on the flash chip and we only have 4 MBytes on some devices for the
bootloader, kernel and rootfs, adding 100 KBytes there is a significant
amount of memory. Instead of adding a initramfs I would like to be able
to define the rootfs somewhere in device tree and not by adding a
bootargs line into device tree. These particular patches are probably
the wrong way, but nobody told me how to do this in a better way.

> Frankly, I don't see a real need for this in the devicetree, other than solving
> someone's particular workflow/use case.