[Buildroot] [PATCH v3] Makefile: fix use of many br2-external trees

[Yann E. MORIN]

Thomas, All,

On 2022-09-21 20:13 +0200, Thomas Petazzoni spake thusly:
> On Tue, 20 Sep 2022 21:46:45 +0200
> "Yann E. MORIN" <yann.morin.1998 at free.fr> wrote:
[--SNIP--]
> > One of the rationale behind this code, is that we want the defconfig
> > files from br2-external trees further down the list, to override
> > defconfig files from those earlier in the list, even overriding the
> > defconfig files from Buildroot itself.
> This is the part I would like to challenge. Why do we want to allow
> BR2_EXTERNAL to override defconfigs from the main tree? We do not allow
> this for packages, why should we allow it for defconfigs?

This patch does not change the actual behaviour: we've been allowing
this for the past 6 years, we've documented it; all that patch does is
actually fix using more than 5 br2-external trees.

> To me, allowing the override of defconfigs is actually a bad idea: when
> you run "make foo_defconfig", it's no longer really clear which
> "foo_defconfig" is really going to be used. Yes, it's well defined, but
> it isn't "obvious".

I think initially, it was far simpler to do it that way, since we did
not have a list of defconfig files, and so we (ab)used make ability to
override a rule, to justify a simpler code on our side.

Changing that behaviour is now easier, now that we do have a list of
defconfig files, but if at all, that should be done in a follow-up
patch.

However, the multi br2-external support is there to cover one case: a
br2-xternal tree provides basic support for a board (e.g. by a team in
charge of the ardware support), and a second br2-external provides
defconfig for an actual product. In this case, given a board named
'foo', it is understanble that the harware guys name their defconfig
foo_defconfig, and that the product team also name their defconfig
foo_defconfig. So, I think allowing this overide is not a bad thing.

Regards,
Yann E. MORIN.

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