[U-Boot] Avoiding Relocation on ARM When Earlier Bootloader Inits RAM?

[Albert ARIBAUD]

Hi Tim,

Le 14/02/2011 18:01, Tim Kryger a écrit :
> Hello,
>
> After looking at code, searching the mailing list archive, and reviewing the git
> commit log, I now understand that for ARM relocation is performed unless U-Boot
> is already running at its final destination as computed within board_init_f.
> Since this computation attempts to back off from the end of RAM the resulting
> address varies when U-Boot changes size.  On my board I have an earlier
> bootloader that initializes RAM.  Presently, it copies U-Boot near the start of
> RAM and lets U-Boot relocate itself to the end.  This is inefficient and I would
> like to eliminate the extra copy.  I suspect that my situation is not unique and
> would be grateful to anyone willing to share their thoughts or experiences on
> how best to deal with this.
>
> Thanks,
> Tim Kryger

What you are looking for requires that the bootloader compute where 
U-Boot should end up in RAM, just like U-Boot would compute it too. It 
certainly is not easy, possibly even impossible due to run-time memory 
allocation from top of RAM before the U-boot location is computed.

Note that even if you can compute the address, you would save a copy, 
but you would still need to go through the relocation code, which takes 
a while too.

Besides, loading U-boot at the lowest location then relocating up is 
doing precisely what the feature is supposed to do: have a single U-Boot 
binary able to run on variants of a board with different amounts of RAM. 
Preloading at a fixed address would defeat the idea.

Amicalement,
-- 
Albert.