[PATCH 2/2] Kbuild: Use dtc's -d (dependency) option

[Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>]

This hooks dtc into Kbuild's dependency system.

Thus, for example, "make dtbs" will rebuild tegra-harmony.dtb if only
tegra20.dtsi has changed yet tegra-harmony.dts has not. The previous
lack of this feature recently caused me to have very confusing "git
bisect" results.

For ARM, it's obvious what to add to $(targets). I'm not familiar enough
with other architectures to know what to add there. Powerpc appears to
already add various .dtb files into $(targets), but the other archs may
need something added to $(targets) to work.

Signed-off-by: Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
---
I have only tested this series for ARM.

 arch/arm/boot/Makefile        |    6 ++++--
 arch/c6x/boot/Makefile        |    2 +-
 arch/microblaze/boot/Makefile |    2 +-
 arch/openrisc/boot/Makefile   |    4 ++--
 arch/powerpc/boot/Makefile    |    4 ++--
 scripts/Makefile.lib          |    2 +-
 6 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/arch/arm/boot/Makefile b/arch/arm/boot/Makefile
index 1338cf0..c72730d 100644
--- a/arch/arm/boot/Makefile
+++ b/arch/arm/boot/Makefile
@@ -62,9 +62,11 @@ $(obj)/zImage-dtb.%:	$(obj)/%.dtb $(obj)/zImage
 
 endif
 
+targets += $(dtb-y)
+
 # Rule to build device tree blobs
-$(obj)/%.dtb: $(src)/dts/%.dts
-	$(call cmd,dtc)
+$(obj)/%.dtb: $(src)/dts/%.dts FORCE
+	$(call if_changed_dep,dtc)
 
 $(obj)/dtbs: $(addprefix $(obj)/, $(dtb-y))
 
diff --git a/arch/c6x/boot/Makefile b/arch/c6x/boot/Makefile
index ecca820..6891257 100644
--- a/arch/c6x/boot/Makefile
+++ b/arch/c6x/boot/Makefile
@@ -13,7 +13,7 @@ obj-y += linked_dtb.o
 endif
 
 $(obj)/%.dtb: $(src)/dts/%.dts FORCE
-	$(call cmd,dtc)
+	$(call if_changed_dep,dtc)
 
 quiet_cmd_cp = CP      $< $@$2
 	cmd_cp = cat $< >$@$2 || (rm -f $@ && echo false)
diff --git a/arch/microblaze/boot/Makefile b/arch/microblaze/boot/Makefile
index 4c4e58e..0c796cf 100644
--- a/arch/microblaze/boot/Makefile
+++ b/arch/microblaze/boot/Makefile
@@ -53,6 +53,6 @@ $(obj)/simpleImage.%: vmlinux FORCE
 DTC_FLAGS := -p 1024
 
 $(obj)/%.dtb: $(src)/dts/%.dts FORCE
-	$(call cmd,dtc)
+	$(call if_changed_dep,dtc)
 
 clean-files += *.dtb simpleImage.*.unstrip linux.bin.ub
diff --git a/arch/openrisc/boot/Makefile b/arch/openrisc/boot/Makefile
index 98ca185..0995835 100644
--- a/arch/openrisc/boot/Makefile
+++ b/arch/openrisc/boot/Makefile
@@ -11,5 +11,5 @@ clean-files := *.dtb.S
 
 #DTC_FLAGS ?= -p 1024
 
-$(obj)/%.dtb: $(src)/dts/%.dts
-	$(call cmd,dtc)
+$(obj)/%.dtb: $(src)/dts/%.dts FORCE
+	$(call if_changed_dep,dtc)
diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile
index 15986e7..8844a17 100644
--- a/arch/powerpc/boot/Makefile
+++ b/arch/powerpc/boot/Makefile
@@ -345,8 +345,8 @@ $(obj)/treeImage.%: vmlinux $(obj)/%.dtb $(wrapperbits)
 	$(call if_changed,wrap,treeboot-$*,,$(obj)/$*.dtb)
 
 # Rule to build device tree blobs
-$(obj)/%.dtb: $(src)/dts/%.dts
-	$(call cmd,dtc)
+$(obj)/%.dtb: $(src)/dts/%.dts FORCE
+	$(call if_changed_dep,dtc)
 
 # If there isn't a platform selected then just strip the vmlinux.
 ifeq (,$(image-y))
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 5d986d9..7bae316 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -264,7 +264,7 @@ $(obj)/%.dtb.S: $(obj)/%.dtb
 	$(call cmd,dt_S_dtb)
 
 quiet_cmd_dtc = DTC     $@
-cmd_dtc = $(objtree)/scripts/dtc/dtc -O dtb -o $@ -b 0 $(DTC_FLAGS) $<
+cmd_dtc = $(objtree)/scripts/dtc/dtc -O dtb -o $@ -b 0 $(DTC_FLAGS) -d $(depfile) $<
 
 # Bzip2
 # ---------------------------------------------------------------------------
-- 
1.7.0.4