kbuild: consolidate Devicetree dtb build rules

There is nothing arch specific about building dtb files other than their
location under /arch/*/boot/dts/. Keeping each arch aligned is a pain.
The dependencies and supported targets are all slightly different.
Also, a cross-compiler for each arch is needed, but really the host
compiler preprocessor is perfectly fine for building dtbs. Move the
build rules to a common location and remove the arch specific ones. This
is done in a single step to avoid warnings about overriding rules.

The build dependencies had been a mixture of 'scripts' and/or 'prepare'.
These pull in several dependencies some of which need a target compiler
(specifically devicetable-offsets.h) and aren't needed to build dtbs.
All that is really needed is dtc, so adjust the dependencies to only be
dtc.

This change enables support 'dtbs_install' on some arches which were
missing the target.

Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Paul Burton <paul.burton@mips.com>
Acked-by: Ley Foon Tan <ley.foon.tan@intel.com>
Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Michal Marek <michal.lkml@markovi.net>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: linux-kbuild@vger.kernel.org
Cc: linux-snps-arc@lists.infradead.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: uclinux-h8-devel@lists.sourceforge.jp
Cc: linux-mips@linux-mips.org
Cc: nios2-dev@lists.rocketboards.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-xtensa@linux-xtensa.org
Signed-off-by: Rob Herring <robh@kernel.org>

1 files changed, 36 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index 19948e556941..021e274c4b03 100644
--- a/Makefile
+++ b/Makefile
@@ -1071,7 +1071,7 @@ include/config/kernel.release: $(srctree)/Makefile FORCE
 # Carefully list dependencies so we do not try to build scripts twice
 # in parallel
 PHONY += scripts
-scripts: scripts_basic asm-generic gcc-plugins $(autoksyms_h)
+scripts: scripts_basic scripts_dtc asm-generic gcc-plugins $(autoksyms_h)
         $(Q)$(MAKE) $(build)=$(@)
 
 # Things we need to do before we recursively start building the kernel
@@ -1216,6 +1216,35 @@ kselftest-merge:
         +$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig
 
 # ---------------------------------------------------------------------------
+# Devicetree files
+
+ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/boot/dts/),)
+dtstree := arch/$(SRCARCH)/boot/dts
+endif
+
+ifneq ($(dtstree),)
+
+%.dtb: prepare3 scripts_dtc
+        $(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
+
+PHONY += dtbs dtbs_install
+dtbs: prepare3 scripts_dtc
+        $(Q)$(MAKE) $(build)=$(dtstree)
+
+dtbs_install:
+        $(Q)$(MAKE) $(dtbinst)=$(dtstree)
+
+ifdef CONFIG_OF_EARLY_FLATTREE
+all: dtbs
+endif
+
+endif
+
+PHONY += scripts_dtc
+scripts_dtc: scripts_basic
+        $(Q)$(MAKE) $(build)=scripts/dtc
+
+# ---------------------------------------------------------------------------
 # Modules
 
 ifdef CONFIG_MODULES
@@ -1424,6 +1453,12 @@ help:
         @echo  '  kselftest-merge - Merge all the config dependencies of kselftest to existing'
         @echo  '                    .config.'
         @echo  ''
+        @$(if $(dtstree), \
+                echo 'Devicetree:'; \
+                echo '* dtbs            - Build device tree blobs for enabled boards'; \
+                echo '  dtbs_install    - Install dtbs to $(INSTALL_DTBS_PATH)'; \
+                echo '')
+
         @echo 'Userspace tools targets:'
         @echo '  use "make tools/help"'
         @echo '  or  "cd tools; make help"'