[PATCH v2] kbuild: add dtbs target for building all dtbs of an ARCH

[Ahmad Fatoum]

As described in the documentation, upstream device trees extended by
barebox should take care to cause compile errors, not runtime errors,
when the paths they extend disappear. This way, breakage can be easily
detected when synchronizing the dts/ directory and fixed right then.

Make this process easier by providing a dtbs target that builds all
device trees available in arch/$(SRCARCH)/dts/.

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
v1 -> v2:
  - populate $(targets) with device trees to build, so make dtbs does
    only build dts files changed since the last make dtbs run (Sascha)
---
 Makefile | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/Makefile b/Makefile
index 906068036715..3bf5cbce32a4 100644
--- a/Makefile
+++ b/Makefile
@@ -998,6 +998,22 @@ include/generated/version.h: FORCE
 include/generated/utsrelease.h: include/config/kernel.release FORCE
 	$(call filechk,utsrelease.h)
 
+# ---------------------------------------------------------------------------
+# Devicetree files
+
+ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/dts/),)
+dtstree := arch/$(SRCARCH)/dts
+endif
+
+ifneq ($(dtstree),)
+
+PHONY += dtbs
+all_dtbs += $(patsubst $(srctree)/%.dts,$(objtree)/%.dtb,$(wildcard $(srctree)/$(dtstree)/*.dts))
+targets += $(all_dtbs)
+dtbs: $(all_dtbs)
+
+endif
+
 # ---------------------------------------------------------------------------
 # Modules
 
@@ -1173,6 +1189,10 @@ help:
 	@$(if $(archhelp),$(archhelp),\
 		echo '  No architecture specific help defined for $(SRCARCH)')
 	@echo  ''
+	@$(if $(dtstree), \
+		echo '  Devicetree:'; \
+		echo '    * dtbs             - Build device tree blobs for all boards'; \
+		echo '')
 	@$(if $(boards), \
 		$(foreach b, $(boards), \
 		printf "  %-24s - Build for %s\\n" $(b) $(subst _defconfig,,$(b));) \
-- 
2.28.0