[ELDK] e500mc target architecture

[Valentin Longchamp]

Hello Wolfgang and Detlev,

(I'm also including the ML since this may be of interest for other that may be
confronted with the same type of question).

We are currently very happy with ELDK 5 (and previously 4), that we use for all
our Linux boards with various architectures (powerpc, powerpc-softfloat and
arvm5te target architectures).

We are now starting a new design which targets the p2041 CPU from Freescale
(QorIQ family) and we want to continue with ELDK for this CPU as well. There has
been earlier last year a prestudy for this new development. During this process,
there was a request from us to add a powerpc-e500v2 target architecture for ELDK
that has now been available since release 5.1 IIRC. Unfortunately, we made a
mistake for that request, and the correct target architecture for the QorIQ
family would be powerpc-e500mc.

The straightforward solution would be to add this target architecture again. But
I would like to know, what you think is the best approach in this case ? Because
of course the generic "powerpc" target architecture produces code that works
perfectly fine on a P2041 CPU as well (I have already tested it on the P2041RDB
dev board). The drawback is that this code does not really takes advantage of
the e500mc cores present in the p2041 cpu. This could however be corrected by
adding the "-mcpu=e500mc -mtune=e500mc" (or only one of them) flags in our
compile flags.

I'm asking because I do not see a lot of variations of PPC cores in the target
architecture lists and that's maybe because the above approach is preferred. The
advantage of the above approach is that you have less binary ELDKs to manage and
maintain. The drawback is that the ELDK binaries in the minimal rootfs then are
not really optimized four our target architecture (by the way, do you have any
idea of the performance improvement that this would give us ?).

If you need further information, please let me know.

Best Regards

Valentin