[U-Boot] [PATCH 5/6] cmd: mtdparts: support runtime generated mtdparts

[Michal Suchanek]

Hello,

On 5 June 2016 at 19:43, Ladislav Michl <ladis at linux-mips.org> wrote:
> Some CPUs contains boot ROM code capable reading first few blocks
> (where SPL resides) of NAND flash and executing it. It is wise to
> create separate partition here for SPL. As block size depends on
> NAND chip used, we could either use worst case (biggest) partition
> size or base its size on actual block size. This patch adds support
> for the latter option.
>

There is similar problem on sunxi.

Given this flash is non-removable and has many pins you are unlikely
going to encounter its content on any system that was not loaded with
u-boot.

Still Linux can only produce fixed size mtdparts. You can prepend
perfectly sized mtdparts for u-boot but until Linux is taught to
follow that with its own partitions without gap you still need to use
the worst case scenario for the start of the Linux partitions.

On sunxi the range of supported block sizes and the size of the
SPL+U-BOOT are not large so this is generally not worth the effort.

If support for this is attempted Linux should be probably taught to
get mtdparts in pages and eraseblocks and then the default mtdparts
can be in those.

If on the other hand you generate the fixed layout for Linux
partitions on the fly and this patch changes how the Linux partitions
are generated it can happen that the Linux partitions are at different
place with different versions of u-boot giving potentially disastrous
results.

Thanks

Miichal