[PATCH V5 1/2] kbuild: centralize .dts->.dtb rule

[Stephen Warren]

From: Stephen Warren <swarren@xxxxxxxxxx>

All architectures that use cmd_dtc do so in the same way. Move the build
rule to a central location to avoid duplication.

Update Documentation/kbuild to remove the explicit call to cmd_dtc from
the example, now that the rule exists in a centralized location, and in
fact replace the example with a couple that still exist.

Signed-off-by: Stephen Warren <swarren@xxxxxxxxxx>
---
v5: Update Documentation/kbuild
v4: No change.
v3: No change.
v2: New patch.
---
 Documentation/kbuild/makefiles.txt |   21 +++++++++++++++------
 arch/arm/boot/Makefile             |    4 ----
 arch/c6x/boot/Makefile             |    3 ---
 arch/openrisc/boot/Makefile        |    3 ---
 arch/powerpc/boot/Makefile         |    4 ----
 scripts/Makefile.lib               |    3 +++
 6 files changed, 18 insertions(+), 20 deletions(-)

diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
index ec9ae67..a0b0671 100644
--- a/Documentation/kbuild/makefiles.txt
+++ b/Documentation/kbuild/makefiles.txt
@@ -1175,15 +1175,24 @@ When kbuild executes, the following steps are followed (roughly):
 	in an init section in the image. Platform code *must* copy the
 	blob to non-init memory prior to calling unflatten_device_tree().
 
+	To use this command, simply add *.dtb into obj-y or targets, or make
+	some other target depend on %.dtb
+
+	A central rule exists to create $(obj)/%.dtb from $(src)/dts/%.dts;
+	architecture Makefiles do no need to explicitly write out that rule.
+
 	Example:
-		#arch/x86/platform/ce4100/Makefile
-		clean-files := *dtb.S
+		#arch/arm/boot/Makefile
+		targets += $(dtb-y)
+		clean-files := *.dtb
+
+		#arch/powerpc/boot/Makefile
+		DTC_FLAGS       ?= -p 1024
 
-		DTC_FLAGS := -p 1024
-		obj-y += foo.dtb.o
+		$(obj)/dtbImage.%: vmlinux $(wrapperbits) $(obj)/%.dtb
+			$(call if_changed,wrap,$*,,$(obj)/$*.dtb)
 
-		$(obj)/%.dtb: $(src)/%.dts
-			$(call cmd,dtc)
+		clean-files += ... *.dtb
 
 --- 6.8 Custom kbuild commands
 
diff --git a/arch/arm/boot/Makefile b/arch/arm/boot/Makefile
index f2aa09e..208bb4c 100644
--- a/arch/arm/boot/Makefile
+++ b/arch/arm/boot/Makefile
@@ -61,10 +61,6 @@ endif
 
 targets += $(dtb-y)
 
-# Rule to build device tree blobs
-$(obj)/%.dtb: $(src)/dts/%.dts FORCE
-	$(call if_changed_dep,dtc)
-
 $(obj)/dtbs: $(addprefix $(obj)/, $(dtb-y))
 
 clean-files := *.dtb
diff --git a/arch/c6x/boot/Makefile b/arch/c6x/boot/Makefile
index 6891257..ad605fb 100644
--- a/arch/c6x/boot/Makefile
+++ b/arch/c6x/boot/Makefile
@@ -12,9 +12,6 @@ ifneq ($(DTB),)
 obj-y += linked_dtb.o
 endif
 
-$(obj)/%.dtb: $(src)/dts/%.dts FORCE
-	$(call if_changed_dep,dtc)
-
 quiet_cmd_cp = CP      $< $@$2
 	cmd_cp = cat $< >$@$2 || (rm -f $@ && echo false)
 
diff --git a/arch/openrisc/boot/Makefile b/arch/openrisc/boot/Makefile
index 0995835..fd329bd 100644
--- a/arch/openrisc/boot/Makefile
+++ b/arch/openrisc/boot/Makefile
@@ -10,6 +10,3 @@ obj-y += $(BUILTIN_DTB)
 clean-files := *.dtb.S
 
 #DTC_FLAGS ?= -p 1024
-
-$(obj)/%.dtb: $(src)/dts/%.dts FORCE
-	$(call if_changed_dep,dtc)
diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile
index 6a15c96..90206f2 100644
--- a/arch/powerpc/boot/Makefile
+++ b/arch/powerpc/boot/Makefile
@@ -356,10 +356,6 @@ $(obj)/treeImage.initrd.%: vmlinux $(obj)/%.dtb $(wrapperbits)
 $(obj)/treeImage.%: vmlinux $(obj)/%.dtb $(wrapperbits)
 	$(call if_changed,wrap,treeboot-$*,,$(obj)/$*.dtb)
 
-# Rule to build device tree blobs
-$(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))
 image-y := vmlinux.strip
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 0be6f11..425578e 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -266,6 +266,9 @@ $(obj)/%.dtb.S: $(obj)/%.dtb
 quiet_cmd_dtc = DTC     $@
 cmd_dtc = $(objtree)/scripts/dtc/dtc -O dtb -o $@ -b 0 $(DTC_FLAGS) -d $(depfile) $<
 
+$(obj)/%.dtb: $(src)/dts/%.dts FORCE
+	$(call if_changed_dep,dtc)
+
 # Bzip2
 # ---------------------------------------------------------------------------
 
-- 
1.7.0.4

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