[RFC][PATCH] kbuild: Produce diff between base DT and U-Boot augmented DT if DEVICE_TREE_DEBUG=1

[Marek Vasut]

In case DEVICE_TREE_DEBUG is set, produce a diff between the base DT and
DT with U-Boot extras, to show how much does the U-Boot DT differ from
the base DT. This is particularly useful together with OF_UPSTREAM, to
minimize the diff between upstream DTs and U-Boot DTs.

Example usage:
$ make r8a779g3_sparrowhawk_defconfig && make DEVICE_TREE_DEBUG=1
$ cat ./dts/upstream/src/arm64/renesas/r8a779g3-sparrow-hawk.dtb.diff

This still has a downside. Even 'dtc -I dts -O dts ...' applied on
base DT and U-Boot augmented DT can produce different phandle IDs
for the same node in those two DTs, which results in a lot of noise
in the resulting diff. The only way I can think of is to patch DTC
to emit full paths in those phandles instead, something like a
phandle = <&{/full/path/to/remote/end} ...>;

Signed-off-by: Marek Vasut <marek.vasut+renesas at mailbox.org>
---
Cc: Adriano Cordova <adrianox at gmail.com>
Cc: Heinrich Schuchardt <xypron.glpk at gmx.de>
Cc: Ilias Apalodimas <ilias.apalodimas at linaro.org>
Cc: Peter Robinson <pbrobinson at gmail.com>
Cc: Sam Edwards <cfsworks at gmail.com>
Cc: Tom Rini <trini at konsulko.com>
Cc: u-boot at lists.denx.de
---
 scripts/Makefile.lib | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 5db2fbc418a..2d8bf3c04f4 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -386,10 +386,31 @@ ifeq ($(CONFIG_OF_LIBFDT_OVERLAY),y)
 DTC_FLAGS += -@
 endif
 
+# In case DEVICE_TREE_DEBUG is set, produce a diff between the base DT and
+# DT with U-Boot extras, to show how much does the U-Boot DT differ from
+# the base DT. This is particularly useful together with OF_UPSTREAM, to
+# minimize the diff between upstream DTs and U-Boot DTs.
+ifdef DEVICE_TREE_DEBUG
+cmd_dtc_diff = \
+	$(HOSTCC) -E $(dtc_cpp_flags) -I$(obj) -x assembler-with-cpp -o $(dtn-tmp) $< ; \
+	$(DTC) -s -O dts -o $@.clean.dts -b 0 \
+		-i $(dir $<) $(DTC_FLAGS) $(dtn-tmp) || \
+		(echo "Check $(shell pwd)/$< for errors" && false); \
+	$(DTC) -s -O dts -o $@.full.dts -b 0 \
+		-i $(dir $<) -i $(u_boot_dtsi_loc) $(DTC_FLAGS) $(dtc-tmp) || \
+		(echo "Check $(shell pwd)/$(pre-tmp) for errors" && false); \
+	(diff -Naru $@.clean.dts $@.full.dts > $@.diff || true)
+
+dtn-tmp = $(subst $(comma),_,$(dot-target).dtn.tmp)
+else
+cmd_dtc_diff =
+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)), \
@@ -400,7 +421,8 @@ cmd_dtc = mkdir -p $(dir ${dtc-tmp}) ; \
 		-d $(depfile).dtc.tmp $(dtc-tmp) || \
 		(echo "Check $(shell pwd)/$(pre-tmp) for errors" && false) \
 		; \
-	sed "s:$(pre-tmp):$(<):" $(depfile).pre.tmp $(depfile).dtc.tmp > $(depfile)
+	sed "s:$(pre-tmp):$(<):" $(depfile).pre.tmp $(depfile).dtc.tmp > $(depfile) ; \
+	$(cmd_dtc_diff)
 
 dtsi_include_list_deps := $(addprefix $(u_boot_dtsi_loc),$(subst $(quote),,$(dtsi_include_list)))
 
-- 
2.51.0