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

On 06/24/2016 08:28 PM, Ezequiel Garcia wrote:

On 18 June 2016 at 16:35, Hauke Mehrtens [off-list ref] wrote:

quoted

On 06/18/2016 09:30 PM, Richard Weinberger wrote:

quoted

Am 18.06.2016 um 21:17 schrieb Hauke Mehrtens:

quoted

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-5/S+JYg5SzeELgA04lAiVw@public.gmane.org>
---
 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.

quoted

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.

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