> From: Casey Connolly <casey.conno...@linaro.org>
> Date: Tue, 10 Jun 2025 18:23:33 +0200
Hi Casey,
> Since we're using the upstream file structure, we know at build time
> the path to each DTB that we build. These same paths are used relative
> to some (maybe version specific) dtb directory on the boot partition
> or ESP.
>
> By recording this path at build time and embedding it into the
> devicetree, we can set the fdtfile environment variable with 100%
> certainty that it is correct.
>
> Devicetree file names are already treated as stable kernel API upstream,
> since they are used by OS loaders extensively.
But when something similar was suggested some time ago, the Linux
kernel folks explicitly stated that the file names are ~*not*
considered to be ABI.
So I think this proposal should be discussed in a broader context,
probably on the devicetree-s...@vger.kernel.org mailing list.
> Embedding the path into the devicetree itself just simplifies the
> process and allows U-Boot or the OS loader to select a devicetree of a
> different version for the specific board that U-Boot is running on.
>
> Signed-off-by: Casey Connolly <casey.conno...@linaro.org>
> ---
> scripts/Makefile.lib | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index
> e89a4a51b74ddccfd9f0a6463cdeded12eaa5235..1f95bda0597c14d2ee785eb8058d607a6c819a56
> 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -360,16 +360,31 @@ $(obj)/%.dtbo.S: $(obj)/%.dtbo
> ifeq ($(CONFIG_OF_LIBFDT_OVERLAY),y)
> DTC_FLAGS += -@
> endif
>
> +ifeq ($(CONFIG_ARM64),y)
> +dt_dir := dts/upstream/src/arm64
> +else
> +dt_dir := dts/upstream/src/$(ARCH)
> +endif
> +
> +ifeq ($(CONFIG_OF_UPSTREAM),y)
> +# Embed the upstream path to the DTB into it as /chosen/fdtfile. This
> property is used
> +# at runtime to set the fdtfile variable
> +dt_extra_snippet = / { chosen { fdtfile = "$(subst $(dt_dir)/,,$@)"; }; };
> +else
> +dt_extra_snippet =
> +endif
> +
> quiet_cmd_dtc = DTC $@
> # Modified for U-Boot
> # Bring in any U-Boot-specific include at the end of the file
> # And finally any custom .dtsi fragments specified with
> CONFIG_DEVICE_TREE_INCLUDES
> cmd_dtc = mkdir -p $(dir ${dtc-tmp}) ; \
> (cat $< > $(pre-tmp)); \
> $(foreach f,$(subst $(quote),,$(dtsi_include_list)
> $(CONFIG_DEVICE_TREE_INCLUDES)), \
> echo '$(pound)include "$(f)"' >> $(pre-tmp);) \
> + [[ -z "$(dt_extra_snippet)" ]] || echo '$(dt_extra_snippet)' >>
> $(pre-tmp); \
> $(HOSTCC) -E $(dtc_cpp_flags) -I$(obj) -x assembler-with-cpp -o
> $(dtc-tmp) $(pre-tmp) ; \
> $(DTC) -O dtb -o $@ -b 0 \
> -i $(dir $<) -i $(u_boot_dtsi_loc) $(DTC_FLAGS) \
> -d $(depfile).dtc.tmp $(dtc-tmp) || \
>
> --
> 2.49.0
>
>
