[PATCH 1/3] dts/upstream: write fdtfile path to /chosen/fdtfile

[Casey Connolly]

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.

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.connolly at 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