[U-Boot] freescale imx bootlets vs u-boot for i.MX28

[Wolfgang Denk]

Dear "Paul B. Henson",

In message <5147B867.5000704 at acm.org> you wrote:
> I'm working on a fairly simple project that needs to boot linux from
> NAND on a freescale i.MX28 platform, and there's a lack of consensus on
> how to handle the boot loader.
>
> One option would be to simply use the stock freescale imx bootlets to
> load the linux kernel, the other to leverage u-boot.

Indeed both are usable approaches that can be taken, and that have
been taken before.

> Clearly u-boot has a lot more functionality and feature set than the
> basic bootlets, but for this project there's really nothing more needed
> from the bootloader then to load the kernel from nand and pass control
> to it, and one faction thinks it would be more efficient just to use the
> bootlets rather than adding u-boot to the mix.

This is true.  But without better knowledge of your project's
requirements it is impossible to us to give any reasonable advice.  If
you will just ship such a system and never really care about it again,
such an approach may work perfectly fine.  If, on the other hand,
you have to consider things like support for service and maintenance
tasks, software updates (especially reliable ones), debugging, etc.,
then you may find bootlets don't offer much support for any such
things.

> Assuming a scenario where the boot loader is expected to just load a
> linux kernel and nothing else, what advantages would u-boot provide over
> the basic bootlets? I know that on some platforms the IPL isn't very

The question is if this scenario (which we often call "production
mode") is really the only possible use you will ever be facing?  Or
will there be other ssituations - say, during development, for
production testing and repair, for maintenance and updates etc., where
you might want to have a more powerful environment?

> good at handling bad blocks or other issues, and having it load a very
> small u-boot which would then be used to load the larger kernel is
> beneficial, but I'm not sure if that's the case for the bootlets.

I guess you have not studied the iMX28 boot ROM code yet?  If so,
consider yourself lucky, and try to leave it at that.  What I heard
from those who did, makes me believe that running U-Boot (or, more
precisely, _any_ code you can control yourself) as quickly as possible
might be a really excellent idea.

Hope this helps.

Best regards,

Wolfgang Denk

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