Re: [PATCH v2] kbuild: fix compilation of dtb specified on command-line without make rule

[Nathan Chancellor <nathan@kernel.org>]

On Wed, Nov 26, 2025 at 11:00:16AM +0100, Thomas De Schampheleire wrote:
> Since commit e7e2941300d2 ("kbuild: split device tree build rules into
> scripts/Makefile.dtbs"), it is no longer possible to compile a device tree
> blob that is not specified in a make rule
> like:
>     dtb-$(CONFIG_FOO) += foo.dtb
> 
> Before the mentioned commit, one could copy a dts file to e.g.
> arch/arm64/boot/dts/ (or a new subdirectory) and then convert it to a dtb
> file using:
>     make ARCH=arm64 foo.dtb
> 
> In this scenario, both 'dtb-y' and 'dtb-' are empty, and the inclusion of
> scripts/Makefile.dtbs relies on 'targets' to contain the MAKECMDGOALS. The
> value of 'targets', however, is only final later in the code.
> 
> Move the conditional include of scripts/Makefile.dtbs down to where the
> value of 'targets' is final. Since Makefile.dtbs updates 'always-y' which is
> used as a prerequisite in the build rule, the build rule also needs to move
> down.
> 
> Fixes: e7e2941300d2 ("kbuild: split device tree build rules into scripts/Makefile.dtbs")
> Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
> ---

Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>

>  scripts/Makefile.build | 26 ++++++++++++++------------
>  1 file changed, 14 insertions(+), 12 deletions(-)
> 
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index d0ee33a487be..82a6e328ceee 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -527,18 +527,6 @@ ifneq ($(userprogs),)
>  include $(srctree)/scripts/Makefile.userprogs
>  endif
>  
> -ifneq ($(need-dtbslist)$(dtb-y)$(dtb-)$(filter %.dtb %.dtb.o %.dtbo.o,$(targets)),)
> -include $(srctree)/scripts/Makefile.dtbs
> -endif
> -
> -# Build
> -# ---------------------------------------------------------------------------
> -
> -$(obj)/: $(if $(KBUILD_BUILTIN), $(targets-for-builtin)) \
> -	 $(if $(KBUILD_MODULES), $(targets-for-modules)) \
> -	 $(subdir-ym) $(always-y)
> -	@:
> -
>  # Single targets
>  # ---------------------------------------------------------------------------
>  
> @@ -568,6 +556,20 @@ FORCE:
>  targets += $(filter-out $(single-subdir-goals), $(MAKECMDGOALS))
>  targets := $(filter-out $(PHONY), $(targets))
>  
> +# Now that targets is fully known, include dtb rules if needed
> +ifneq ($(need-dtbslist)$(dtb-y)$(dtb-)$(filter %.dtb %.dtb.o %.dtbo.o,$(targets)),)
> +include $(srctree)/scripts/Makefile.dtbs
> +endif
> +
> +# Build
> +# Needs to be after the include of Makefile.dtbs, which updates always-y
> +# ---------------------------------------------------------------------------
> +
> +$(obj)/: $(if $(KBUILD_BUILTIN), $(targets-for-builtin)) \
> +	 $(if $(KBUILD_MODULES), $(targets-for-modules)) \
> +	 $(subdir-ym) $(always-y)
> +	@:
> +
>  # Read all saved command lines and dependencies for the $(targets) we
>  # may be building above, using $(if_changed{,_dep}). As an
>  # optimization, we don't need to read them if the target does not
> 
> base-commit: deab487e0f9b39ae4603e22d7d00908ebfc9753c
> -- 
> 2.51.0
>