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

[Niklas Cassel via buildroot <buildroot@buildroot.org>]

[replying from an email address that is subscribed this time...]

On Fri, Dec 13, 2024 at 09:53:27AM +0100, Michael Walle wrote:
> 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


> 
> 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.


Kind regards,
Niklas
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