[U-Boot-Users] u-boot and Linux kernel forward compatibility is unsure?

[Wolfgang Denk]

Dear Leon,

in message <c384c5ea0805281514r1740072fw7c49101a4535f818 at mail.gmail.com> you wrote:
> 
> triggered by the e-mail below (which solved my issue, thanks Kim) I
> have the following question:
> 
> For how long can I expect current u-boot (say 1.3.4) to be forward
> compatible with newer Linux kernels?

I think chances are pretty good. Please keep in mind that we're right
in the middle of a really big change - the merging  of  the  arch/ppc
and arch/ppc64 code into a common arch/powerpc tree is something that
hits  many  areas  pretty  heavily, and the device tree support which
many things depend upon is still a (fast) moving target.

But even today you can build a current Linux kernel using the cuImage
wrapper and boot it on an old (say, version 1.2.0) U-Boot.


Please do not confuse compatibility with "having all the latest and
greatest new interfaces as well". 

I think you have to get used to the thought that the Linux kernel  is
undergoing serious changes right now (which means you cannot consider
it  stable  enough to use the latest version in a project where long-
term compatibility is an issue).

> It seems the u-boot from only half a year old cannot boot a current
> Linux kernel (!).

Only if you try to use the latest features. Use  a  cuImage,  and  it
should just work fine.

> I typically work on products where the initial boot loader is adapted
> to provide fail-safe upgrades and itself is never upgraded to prevent
> the chance of non-flashable (bricked) products in the very small
> chance something goes wrong during the boot loader update.

Been there, too.

> How do people deal with using u-boot in a fail-safe environment where
> the chance of brickage must be zero and the (initial) bootloader
> itself cannot be updated?

You will probably have to accept that software updates are restricted
to certain versions. If you started with a  root  file  system  build
around  a  2.4  Linux  kernel,  you  will probably have problems when
trying to use a current 2.6 kernel with this  file  system  image  as
well.  There  may  (or  may  not)  be  compatibility layers (like the
cuImage wrapper) that extend that period, but there is no guarantee.

> Should I plan for a second stage loader?

You already have one - Linux. Use kexec if you really think you must.

> Also, is there any plan to add fail-safe features to u-boot?

What are you thinking of?

Best regards,

Wolfgang Denk

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