[PATCH 0/4] V3 Add ability to link device blob(s) into vmlinux

[PATCH 0/4] V3 Add ability to link device blob(s) into vmlinux

[dirk.brandewie]

From: Dirk Brandewie <dirk.brandewie@gmail.com>

This patch set adds the ability to link device tree blobs into
vmlinux. 

Patch 1 implements the changes to include/asm-generic/vmlinux.lds.h and
adds a generic rule for generating DTB objects to be linked vmlinux.

Patch 2 implements linking a DTB into an x86 image.

Patch 3-4 move {powerpc,microblaze}/boot/Makefile to use the dtc rule
in patch 1.

This patch set has been tested on x86.

Powerpc and Microblaze have been compile tested with and without patch
3 and 4 applied.

Changes from V1:

Documentation added for dtc command in Makefile.lib to
Documentation/kbuild/makefiles.txt
Separate DTB_ALIGNMENT define removed.
FORCE removed from dtc rule.
Removed hardcoded path to dts files from dtc command.  
Moved %.dtb: %.dts rule to arch specific makefiles. 
 
Patch for adding kernel command line option to pass in dtb_compat
string dropped from this set will be submitted seperately.

Changes from V2:

Rule to create assembly wrapper for blob changed to use Sam Ravnborgs
suggested implementation.

Rules in architecture specific Makefiles changed to use the cmd
function instead of the if_changed function.

Dirk Brandewie (4):
  of: Add support for linking device tree blobs into vmlinux
  x86/of: Add building device tree blob(s) into image.
  of/powerpc: Use generic rule to build dtb's
  microblaze/of: Use generic rule to build dtb's

 Documentation/kbuild/makefiles.txt |   15 +++++++++++++++
 arch/microblaze/boot/Makefile      |   12 +++---------
 arch/powerpc/boot/Makefile         |    8 +++-----
 arch/x86/platform/ce4100/Makefile  |   10 ++++++++++
 include/asm-generic/vmlinux.lds.h  |   13 +++++++++++--
 scripts/Makefile.lib               |   23 +++++++++++++++++++++++
 6 files changed, 65 insertions(+), 16 deletions(-)

-- 
1.7.2.3

[PATCH 1/4] of: Add support for linking device tree blobs into vmlinux

[dirk.brandewie]

From: Dirk Brandewie <dirk.brandewie@gmail.com>

This patch adds support for linking device tree blob(s) into
vmlinux. Modifies asm-generic/vmlinux.lds.h to add linking
.dtb sections into vmlinux. To maintain compatiblity with the of/fdt
driver code platforms MUST copy the blob to a non-init memory location
before the kernel frees the .init.* sections in the image.

Modifies scripts/Makefile.lib to add a kbuild command to
compile DTS files to device tree blobs and a rule to create objects to
wrap the blobs for linking.

STRUCT_ALIGNMENT is defined in vmlinux.lds.h for use in the rule to
create wrapper objects for the dtb in Makefile.lib.  The
STRUCT_ALIGN() macro in vmlinux.lds.h is modified to use the
STRUCT_ALIGNMENT definition.

The DTB's are placed on 32 byte boundries to allow parsing the blob
with driver/of/fdt.c during early boot without having to copy the blob
to get the structure alignment GCC expects.

A DTB is linked in by adding the DTB object to the list of objects to
be linked into vmlinux in the archtecture specific Makefile using
   obj-y += foo.dtb.o

Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>
---
 Documentation/kbuild/makefiles.txt |   15 +++++++++++++++
 include/asm-generic/vmlinux.lds.h  |   13 +++++++++++--
 scripts/Makefile.lib               |   23 +++++++++++++++++++++++
 3 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
index 0ef00bd..86e3cd0 100644
--- a/Documentation/kbuild/makefiles.txt
+++ b/Documentation/kbuild/makefiles.txt
@@ -1136,6 +1136,21 @@ When kbuild executes, the following steps are followed (roughly):
 	      resulting in the target file being recompiled for no
 	      obvious reason.
 
+    dtc
+	Create flattend device tree blob object suitable for linking
+	into vmlinux. Device tree blobs linked into vmlinux are placed
+	in an init section in the image. Platform code *must* copy the
+	blob to non-init memory prior to calling unflatten_device_tree().
+
+	Example:
+		#arch/x86/platform/ce4100/Makefile
+		clean-files := *dtb.S
+
+		DTC_FLAGS := -p 1024
+		obj-y += foo.dtb.o
+
+		$(obj)/%.dtb: $(src)/%.dts
+			$(call cmd,dtc)
 
 --- 6.7 Custom kbuild commands
 
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index bd69d79..05cbad0 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -67,7 +67,8 @@
  * Align to a 32 byte boundary equal to the
  * alignment gcc 4.5 uses for a struct
  */
-#define STRUCT_ALIGN() . = ALIGN(32)
+#define STRUCT_ALIGNMENT 32
+#define STRUCT_ALIGN() . = ALIGN(STRUCT_ALIGNMENT)
 
 /* The actual configuration determine if the init/exit sections
  * are handled as text/data or they can be discarded (which
@@ -146,6 +147,13 @@
 #define TRACE_SYSCALLS()
 #endif
 
+
+#define KERNEL_DTB()							\
+	STRUCT_ALIGN();							\
+	VMLINUX_SYMBOL(__dtb_start) = .;				\
+	*(.dtb.init.rodata)						\
+	VMLINUX_SYMBOL(__dtb_end) = .;
+
 /* .data section */
 #define DATA_DATA							\
 	*(.data)							\
@@ -468,7 +476,8 @@
 	MCOUNT_REC()							\
 	DEV_DISCARD(init.rodata)					\
 	CPU_DISCARD(init.rodata)					\
-	MEM_DISCARD(init.rodata)
+	MEM_DISCARD(init.rodata)					\
+	KERNEL_DTB()
 
 #define INIT_TEXT							\
 	*(.init.text)							\
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 4c72c11..63b287c 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -200,6 +200,29 @@ quiet_cmd_gzip = GZIP    $@
 cmd_gzip = (cat $(filter-out FORCE,$^) | gzip -f -9 > $@) || \
 	(rm -f $@ ; false)
 
+# DTC
+#  ---------------------------------------------------------------------------
+
+# Generate an assembly file to wrap the output of the device tree compiler
+quiet_cmd_dt_S_dtb= DTB    $@
+cmd_dt_S_dtb=						\
+(							\
+	echo '\#include <asm-generic/vmlinux.lds.h>'; 	\
+	echo '.section .dtb.init.rodata,"a"';		\
+	echo '.balign STRUCT_ALIGNMENT';                \
+	echo '.global __dtb_$(*F)_begin';               \
+	echo '__dtb_$(*F)_begin:';                      \
+	echo '.incbin "$<" ';                           \
+	echo '__dtb_$(*F)_end:';                        \
+	echo '.global __dtb_$(*F)_end';                 \
+	echo '.balign STRUCT_ALIGNMENT'; 		\
+) > $@
+
+$(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) $<
 
 # Bzip2
 # ---------------------------------------------------------------------------
-- 
1.7.2.3

[PATCH 2/4] x86/of: Add building device tree blob(s) into image.

[dirk.brandewie]

From: Dirk Brandewie <dirk.brandewie@gmail.com>

This patch adds linking device tree blob into vmlinux. DTB's are
added by adding the blob object name to list of objects to be linked
into the image.

Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>
---
 arch/x86/platform/ce4100/Makefile |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/arch/x86/platform/ce4100/Makefile b/arch/x86/platform/ce4100/Makefile
index 91fc929..e5f3b7b 100644
--- a/arch/x86/platform/ce4100/Makefile
+++ b/arch/x86/platform/ce4100/Makefile
@@ -1 +1,11 @@
 obj-$(CONFIG_X86_INTEL_CE)	+= ce4100.o
+clean-files := *dtb.S
+
+ifdef CONFIG_X86_OF
+###
+# device tree blob
+obj-$(CONFIG_X86_INTEL_CE) += ce4100.dtb.o
+
+$(obj)/%.dtb: $(src)/%.dts
+	$(call cmd,dtc)
+endif
-- 
1.7.2.3

[PATCH 3/4] of/powerpc: Use generic rule to build dtb's

[dirk.brandewie]

From: Dirk Brandewie <dirk.brandewie@gmail.com>

Modify arch/powerpc/boot/Makefile to use dtc command in
scripts/Makefile.lib

Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>
---
 arch/powerpc/boot/Makefile |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile
index fae8192..96deec6 100644
--- a/arch/powerpc/boot/Makefile
+++ b/arch/powerpc/boot/Makefile
@@ -35,7 +35,7 @@ endif
 
 BOOTCFLAGS	+= -I$(obj) -I$(srctree)/$(obj)
 
-DTS_FLAGS	?= -p 1024
+DTC_FLAGS	?= -p 1024
 
 $(obj)/4xx.o: BOOTCFLAGS += -mcpu=405
 $(obj)/ebony.o: BOOTCFLAGS += -mcpu=405
@@ -332,10 +332,8 @@ $(obj)/treeImage.%: vmlinux $(obj)/%.dtb $(wrapperbits)
 	$(call if_changed,wrap,treeboot-$*,,$(obj)/$*.dtb)
 
 # Rule to build device tree blobs
-DTC = $(objtree)/scripts/dtc/dtc
-
-$(obj)/%.dtb: $(dtstree)/%.dts
-	$(DTC) -O dtb -o $(obj)/$*.dtb -b 0 $(DTS_FLAGS) $(dtstree)/$*.dts
+$(obj)/%.dtb: $(src)/dts/%.dts
+	$(call cmd,dtc)
 
 # If there isn't a platform selected then just strip the vmlinux.
 ifeq (,$(image-y))
-- 
1.7.2.3

[PATCH 4/4] microblaze/of: Use generic rule to build dtb's

[dirk.brandewie]

From: Dirk Brandewie <dirk.brandewie@gmail.com>

Modify arch/powerpc/boot/Makefile to use dtc command in
scripts/Makefile.lib

Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>
---
 arch/microblaze/boot/Makefile |   12 +++---------
 1 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/arch/microblaze/boot/Makefile b/arch/microblaze/boot/Makefile
index be01d78..4c4e58e 100644
--- a/arch/microblaze/boot/Makefile
+++ b/arch/microblaze/boot/Makefile
@@ -10,9 +10,6 @@ targets := linux.bin linux.bin.gz simpleImage.%
 
 OBJCOPYFLAGS := -O binary
 
-# Where the DTS files live
-dtstree         := $(srctree)/$(src)/dts
-
 # Ensure system.dtb exists
 $(obj)/linked_dtb.o: $(obj)/system.dtb
 
@@ -51,14 +48,11 @@ $(obj)/simpleImage.%: vmlinux FORCE
 	$(call if_changed,strip)
 	@echo 'Kernel: $@ is ready' ' (#'`cat .version`')'
 
-# Rule to build device tree blobs
-DTC = $(objtree)/scripts/dtc/dtc
 
 # Rule to build device tree blobs
-quiet_cmd_dtc = DTC     $@
-	cmd_dtc = $(DTC) -O dtb -o $(obj)/$*.dtb -b 0 -p 1024 $(dtstree)/$*.dts
+DTC_FLAGS := -p 1024
 
-$(obj)/%.dtb: $(dtstree)/%.dts FORCE
-	$(call if_changed,dtc)
+$(obj)/%.dtb: $(src)/dts/%.dts FORCE
+	$(call cmd,dtc)
 
 clean-files += *.dtb simpleImage.*.unstrip linux.bin.ub
-- 
1.7.2.3

Re: [PATCH 0/4] V3 Add ability to link device blob(s) into vmlinux

[Dirk Brandewie]

On 12/08/2010 07:01 AM, dirk.brandewie@gmail.com wrote:
> From: Dirk Brandewie<dirk.brandewie@gmail.com>
>
> This patch set adds the ability to link device tree blobs into
> vmlinux.
>
> Patch 1 implements the changes to include/asm-generic/vmlinux.lds.h and
> adds a generic rule for generating DTB objects to be linked vmlinux.
>
> Patch 2 implements linking a DTB into an x86 image.
>
> Patch 3-4 move {powerpc,microblaze}/boot/Makefile to use the dtc rule
> in patch 1.
>
> This patch set has been tested on x86.
>
> Powerpc and Microblaze have been compile tested with and without patch
> 3 and 4 applied.
>
> Changes from V1:
>
> Documentation added for dtc command in Makefile.lib to
> Documentation/kbuild/makefiles.txt
> Separate DTB_ALIGNMENT define removed.
> FORCE removed from dtc rule.
> Removed hardcoded path to dts files from dtc command.
> Moved %.dtb: %.dts rule to arch specific makefiles.
>
> Patch for adding kernel command line option to pass in dtb_compat
> string dropped from this set will be submitted seperately.
>
> Changes from V2:
>
> Rule to create assembly wrapper for blob changed to use Sam Ravnborgs
> suggested implementation.
>
> Rules in architecture specific Makefiles changed to use the cmd
> function instead of the if_changed function.
>
> Dirk Brandewie (4):
>    of: Add support for linking device tree blobs into vmlinux
>    x86/of: Add building device tree blob(s) into image.
>    of/powerpc: Use generic rule to build dtb's
>    microblaze/of: Use generic rule to build dtb's
>
>   Documentation/kbuild/makefiles.txt |   15 +++++++++++++++
>   arch/microblaze/boot/Makefile      |   12 +++---------
>   arch/powerpc/boot/Makefile         |    8 +++-----
>   arch/x86/platform/ce4100/Makefile  |   10 ++++++++++
>   include/asm-generic/vmlinux.lds.h  |   13 +++++++++++--
>   scripts/Makefile.lib               |   23 +++++++++++++++++++++++
>   6 files changed, 65 insertions(+), 16 deletions(-)
>

Any Comments on this patch set?

--Dirk

Re: [PATCH 2/4] x86/of: Add building device tree blob(s) into image.

[Michal Marek]

On 8.12.2010 16:01, dirk.brandewie@gmail.com wrote:
> From: Dirk Brandewie <dirk.brandewie@gmail.com>
> 
> This patch adds linking device tree blob into vmlinux. DTB's are
> added by adding the blob object name to list of objects to be linked
> into the image.
> 
> Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>
> ---
>  arch/x86/platform/ce4100/Makefile |   10 ++++++++++
>  1 files changed, 10 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/platform/ce4100/Makefile b/arch/x86/platform/ce4100/Makefile
> index 91fc929..e5f3b7b 100644
> --- a/arch/x86/platform/ce4100/Makefile
> +++ b/arch/x86/platform/ce4100/Makefile
> @@ -1 +1,11 @@
>  obj-$(CONFIG_X86_INTEL_CE)	+= ce4100.o
> +clean-files := *dtb.S
> +
> +ifdef CONFIG_X86_OF
> +###
> +# device tree blob
> +obj-$(CONFIG_X86_INTEL_CE) += ce4100.dtb.o
> +
> +$(obj)/%.dtb: $(src)/%.dts
> +	$(call cmd,dtc)
> +endif

Hi,

CONFIG_X86_OF should be defined in some Kconfig file and there is no
ce4100.dts??

Michal

Re: [PATCH 1/4] of: Add support for linking device tree blobs into vmlinux

[Michal Marek]

On 8.12.2010 16:01, dirk.brandewie@gmail.com wrote:
> +quiet_cmd_dt_S_dtb= DTB    $@

> +quiet_cmd_dtc = DTC $@

Hi,

just an aesthetic remark: The target name should start at the 9th
column, so there should be 5 spaces after both "DTB" and "DTC".

Michal

Re: [PATCH 1/4] of: Add support for linking device tree blobs into vmlinux

[Dirk Brandewie]

On 12/21/2010 06:24 AM, Michal Marek wrote:
> On 8.12.2010 16:01, dirk.brandewie@gmail.com wrote:
>> +quiet_cmd_dt_S_dtb= DTB    $@
>
>> +quiet_cmd_dtc = DTC $@
>
> Hi,
>
> just an aesthetic remark: The target name should start at the 9th
> column, so there should be 5 spaces after both "DTB" and "DTC".
>
> Michal
Thanks I will fix this.

--Dirk

Re: [PATCH 3/4] of/powerpc: Use generic rule to build dtb's

[Grant Likely]

On Wed, Dec 22, 2010 at 11:57:28AM -0800, dirk.brandewie@gmail.com wrote:
> From: Dirk Brandewie <dirk.brandewie@gmail.com>
> 
> Modify arch/powerpc/boot/Makefile to use dtc command in
> scripts/Makefile.lib
> 
> Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>

applied, thanks

g.

> ---
>  arch/powerpc/boot/Makefile |    8 +++-----
>  1 files changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile
> index fae8192..96deec6 100644
> --- a/arch/powerpc/boot/Makefile
> +++ b/arch/powerpc/boot/Makefile
> @@ -35,7 +35,7 @@ endif
>  
>  BOOTCFLAGS	+= -I$(obj) -I$(srctree)/$(obj)
>  
> -DTS_FLAGS	?= -p 1024
> +DTC_FLAGS	?= -p 1024
>  
>  $(obj)/4xx.o: BOOTCFLAGS += -mcpu=405
>  $(obj)/ebony.o: BOOTCFLAGS += -mcpu=405
> @@ -332,10 +332,8 @@ $(obj)/treeImage.%: vmlinux $(obj)/%.dtb $(wrapperbits)
>  	$(call if_changed,wrap,treeboot-$*,,$(obj)/$*.dtb)
>  
>  # Rule to build device tree blobs
> -DTC = $(objtree)/scripts/dtc/dtc
> -
> -$(obj)/%.dtb: $(dtstree)/%.dts
> -	$(DTC) -O dtb -o $(obj)/$*.dtb -b 0 $(DTS_FLAGS) $(dtstree)/$*.dts
> +$(obj)/%.dtb: $(src)/dts/%.dts
> +	$(call cmd,dtc)
>  
>  # If there isn't a platform selected then just strip the vmlinux.
>  ifeq (,$(image-y))
> -- 
> 1.7.2.3
> 
> --
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[PATCH 3/4] of/powerpc: Use generic rule to build dtb's

[dirk.brandewie]

From: Dirk Brandewie <dirk.brandewie@gmail.com>

Modify arch/powerpc/boot/Makefile to use dtc command in
scripts/Makefile.lib

Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>
---
 arch/powerpc/boot/Makefile |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile
index fae8192..96deec6 100644
--- a/arch/powerpc/boot/Makefile
+++ b/arch/powerpc/boot/Makefile
@@ -35,7 +35,7 @@ endif
 
 BOOTCFLAGS	+= -I$(obj) -I$(srctree)/$(obj)
 
-DTS_FLAGS	?= -p 1024
+DTC_FLAGS	?= -p 1024
 
 $(obj)/4xx.o: BOOTCFLAGS += -mcpu=405
 $(obj)/ebony.o: BOOTCFLAGS += -mcpu=405
@@ -332,10 +332,8 @@ $(obj)/treeImage.%: vmlinux $(obj)/%.dtb $(wrapperbits)
 	$(call if_changed,wrap,treeboot-$*,,$(obj)/$*.dtb)
 
 # Rule to build device tree blobs
-DTC = $(objtree)/scripts/dtc/dtc
-
-$(obj)/%.dtb: $(dtstree)/%.dts
-	$(DTC) -O dtb -o $(obj)/$*.dtb -b 0 $(DTS_FLAGS) $(dtstree)/$*.dts
+$(obj)/%.dtb: $(src)/dts/%.dts
+	$(call cmd,dtc)
 
 # If there isn't a platform selected then just strip the vmlinux.
 ifeq (,$(image-y))
-- 
1.7.2.3

[PATCH 3/4] of/powerpc: Use generic rule to build dtb's

[dirk.brandewie]

From: Dirk Brandewie <dirk.brandewie@gmail.com>

Modify arch/powerpc/boot/Makefile to use dtc command in
scripts/Makefile.lib

Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>
---
 arch/powerpc/boot/Makefile |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile
index fae8192..3afb33a 100644
--- a/arch/powerpc/boot/Makefile
+++ b/arch/powerpc/boot/Makefile
@@ -35,7 +35,7 @@ endif
 
 BOOTCFLAGS	+= -I$(obj) -I$(srctree)/$(obj)
 
-DTS_FLAGS	?= -p 1024
+DTC_FLAGS	?= -p 1024
 
 $(obj)/4xx.o: BOOTCFLAGS += -mcpu=405
 $(obj)/ebony.o: BOOTCFLAGS += -mcpu=405
@@ -332,10 +332,8 @@ $(obj)/treeImage.%: vmlinux $(obj)/%.dtb $(wrapperbits)
 	$(call if_changed,wrap,treeboot-$*,,$(obj)/$*.dtb)
 
 # Rule to build device tree blobs
-DTC = $(objtree)/scripts/dtc/dtc
-
-$(obj)/%.dtb: $(dtstree)/%.dts
-	$(DTC) -O dtb -o $(obj)/$*.dtb -b 0 $(DTS_FLAGS) $(dtstree)/$*.dts
+$(obj)/%.dtb: $(src)/dts/%.dts
+	$(call if_changed,dtc)
 
 # If there isn't a platform selected then just strip the vmlinux.
 ifeq (,$(image-y))
-- 
1.7.2.3

[PATCH 3/4] of/powerpc: Use generic rule to build dtb's

[dirk.brandewie]

From: Dirk Brandewie <dirk.brandewie@gmail.com>

Modify arch/powerpc/boot/Makefile to use dtc command in
scripts/Makefile.lib

Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>
---
 arch/powerpc/boot/Makefile |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile
index fae8192..3afb33a 100644
--- a/arch/powerpc/boot/Makefile
+++ b/arch/powerpc/boot/Makefile
@@ -35,7 +35,7 @@ endif
 
 BOOTCFLAGS	+= -I$(obj) -I$(srctree)/$(obj)
 
-DTS_FLAGS	?= -p 1024
+DTC_FLAGS	?= -p 1024
 
 $(obj)/4xx.o: BOOTCFLAGS += -mcpu=405
 $(obj)/ebony.o: BOOTCFLAGS += -mcpu=405
@@ -332,10 +332,8 @@ $(obj)/treeImage.%: vmlinux $(obj)/%.dtb $(wrapperbits)
 	$(call if_changed,wrap,treeboot-$*,,$(obj)/$*.dtb)
 
 # Rule to build device tree blobs
-DTC = $(objtree)/scripts/dtc/dtc
-
-$(obj)/%.dtb: $(dtstree)/%.dts
-	$(DTC) -O dtb -o $(obj)/$*.dtb -b 0 $(DTS_FLAGS) $(dtstree)/$*.dts
+$(obj)/%.dtb: $(src)/dts/%.dts
+	$(call if_changed,dtc)
 
 # If there isn't a platform selected then just strip the vmlinux.
 ifeq (,$(image-y))
-- 
1.7.2.3