[U-Boot] using different architecture / toolchain for SPL build

[Wolfgang Denk]

Dear Allen,

In message <3C7A7ACA8617D24290826EC008B5CD08510F030F95 at HQMAIL03.nvidia.com> you wrote:
> 
> The tegra build of u-boot currently is a single image that executes
> on both the arm7tdmi and cortex A9, but it's quite fragile because we
> use a armv7 toolchain and have be careful about compiler options and
> ifdefing around inline assembly so it still boots on the arm7tdmi.
> 
> I'm looking at using an SPL build of u-boot that executes only on the
> arm7tdmi and initializes the bare minimum to bring up the A9 and
> transfer control to it. However all the SPL examples I'm looking at
> assume the same toolchain and architecture for the SPL and normal
> u-boot build.

I think you make an important mistake here: please so not mix up "tool
chain" on one side and "build options" on the other side.

> How would others feel about a CROSS_COMPILE_SPL variable that allowed
> one to override the toolchain used during the SPL build?

This makes no sense to me.  The need to use a specific tool chain for
some SoC type usuallyonly comes into play when dealing with user space
code, i. e. when you have to make sure that you also use libraries
that were built with appropriate options.  U-Boot however is pretty
much self-contained - if you are careful (see USE_PRIVATE_LIBGCC) we
do not even depend on the compiler-provided libraries.

All you should have to do is making sure the build is done using
appropriate build options.  I can see no reason why different tool
chains would be needed (not to mention that such an approch would be
a maintainance nightmare for all involved parties).

> The architecture seems harder to fix.  It seems like I really have to
> have two entries in boards.cfg, which means two passes of config/make.

This should be not needed; I also do not think this would be an
acceptable approach.


Best regards,

Wolfgang Denk

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