Re: [Buildroot] [PATCH v3 1/2] linux: add support for device tree overlays

[Michael Walle via buildroot <buildroot@buildroot.org>]

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Hi Niklas,

> > > -Dropped support for out-of-tree device tree overlays, as Linux 6.12 no
> > >  longer supports building an out-of-tree device tree by simply copying
> > >  it to the kernel source directory (without also modifying the Makefile).
> > 
> > Why is that? As it seems, it is not possible to compile it by simply
> > copying to arch/<arch>/dts (which is buildroot doing currently)
> > anymore. But copying it to arch/<arch>/dts/<vendor>/ is working.
> > Correct?
>
> I'm assuming that neither works anymore, see:
> https://lore.kernel.org/buildroot/CAFOYHZDQmMRuK76TpOSAOFPdqAb4gpw=LNKfmpu=sqAD1EMhFg@mail.gmail.com/T/#u
> https://lore.kernel.org/all/CAK7LNAR4h6NZ+D0BK+q4VQBeHWpjzRBQFQ9ovBrftM=6dHRcUg@mail.gmail.com/
> https://lore.kernel.org/buildroot/Z1nq_gneO4ORw3EG@curiosity/T/#t

Thanks for the pointers.

But I've just tested both compiling .dts and .dtso from within a
vendor directory and it seems to be working on next-20241213 (?).

> > In that case, we should work on getting support for that in
> > buildroot as well. Esp. buildroot is really lacking copying an
> > actual device tree into that subdir too and currently it's a PITA to
> > include a soc.dtsi for example. If you're using a device tree in
> > buildroot you'd have to use '#include "vendor/soc.dtsi"' while in
> > the kernel (as well as in yocto) you'll just use '#include
> > "soc.dtsi"'.
>
> Yes, it appears that buildroot folks have an idea that it should be possible to
> restore BR2_LINUX_KERNEL_CUSTOM_DTS_PATH in newer kernels by sed:ing the
> Makefile.
>
> However, I don't see any reason to defer this patch until then.
>
>
> Once someone has written a patch that restores BR2_LINUX_KERNEL_CUSTOM_DTS_PATH
> support for recent kernels, you can submit an incremental path on top of this
> that adds support for out-of-tree device tree overlays, if you so wish.
>
> But honestly, considering that the only buildroot configurations that make use of
> BR2_LINUX_KERNEL_CUSTOM_DTS_PATH are:
> - acmesystems_acqua_a5_256mb_defconfig (v6.6)
> - acmesystems_acqua_a5_512mb_defconfig (v6.6)
> - octavo_osd32mp1_brk_defconfig (v5.10)   
> - octavo_osd32mp1_red_defconfig (v5.10)
> - s6lx9_microboard_defconfig (v4.4.7)
>
> are using really old kernel versions, nothing is broken in upstream buildroot,
> so I expect that it might take quite a long time before anyone bothers to
> restore BR2_LINUX_KERNEL_CUSTOM_DTS_PATH support in newer kernels.

This is most useful for buildroot externals which you cannot grep
that easily :) Thus I'd imagine it is more common than you think.

-michael

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