nios2: use common rules to build built-in dtb

Using the common build support for built-in dtb files just requires
adding a .dtb.o target to obj-y.

This has the side effect that CONFIG_NIOS2_DTB_SOURCE should now be just
the dts filename in arch/nios2/boot/dts/ directory. Before any path was
supported, but if you want to build in your dtb to the kernel, it should
be in the kernel tree.

Cc: Ley Foon Tan <lftan@altera.com>
Cc: nios2-dev@lists.rocketboards.org
Signed-off-by: Rob Herring <robh@kernel.org>

arch/nios2/Makefile

@@ -49,16 +49,14 @@ BOOT_TARGETS = vmImage zImage
 PHONY += $(BOOT_TARGETS) install
 KBUILD_IMAGE := $(nios2-boot)/vmImage
 
-ifneq ($(CONFIG_NIOS2_DTB_SOURCE),"")
-	core-y	+= $(nios2-boot)/
-endif
+core-y	+= $(nios2-boot)/dts/
 
 all: vmImage
 
 archclean:
 	$(Q)$(MAKE) $(clean)=$(nios2-boot)
 
-%.dtb: | scripts
+%.dtb %.dtb.S %.dtb.o: | scripts
 	$(Q)$(MAKE) $(build)=$(nios2-boot)/dts $(nios2-boot)/dts/$@
 
 dtbs:

arch/nios2/boot/Makefile

@@ -31,20 +31,6 @@ $(obj)/zImage: $(obj)/compressed/vmlinux FORCE
 $(obj)/compressed/vmlinux: $(obj)/vmlinux.gz FORCE
 	$(Q)$(MAKE) $(build)=$(obj)/compressed $@
 
-# Rule to build device tree blobs
-DTB_SRC := $(patsubst "%",%,$(CONFIG_NIOS2_DTB_SOURCE))
-
-# Make sure the generated dtb gets removed during clean
-extra-$(CONFIG_NIOS2_DTB_SOURCE_BOOL) += system.dtb
-
-$(obj)/system.dtb: $(DTB_SRC) FORCE
-	$(call cmd,dtc)
-
-# Ensure system.dtb exists
-$(obj)/linked_dtb.o: $(obj)/system.dtb
-
-obj-$(CONFIG_NIOS2_DTB_SOURCE_BOOL) += linked_dtb.o
-
 targets += $(dtb-y)
 
 $(obj)/dtbs: $(addprefix $(obj)/, $(dtb-y))

arch/nios2/boot/dts/Makefile

@@ -1 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0
+
+obj-y := $(patsubst "%.dts",%.dtb.o,$(CONFIG_NIOS2_DTB_SOURCE))