dts: Add alternative location for upstream DTB builds

Allow platform owners to mirror devicetree files from devitree-rebasing
directory into dts/upstream/src/$(ARCH) (special case for arm64). Then
build then along with any *-u-boot.dtsi file present in arch/$(ARCH)/dts
directory. Also add a new Makefile for arm64.

This will help easy migration for platforms which currently are compliant
with upstream Linux kernel devicetree files.

Signed-off-by: Sumit Garg <sumit.garg@linaro.org>

3 files changed, 44 insertions, 3 deletions

diff --git a/dts/Kconfig b/dts/Kconfig
index 00c0aef..09789d3 100644
--- a/dts/Kconfig
+++ b/dts/Kconfig
@@ -85,6 +85,22 @@ config OF_LIVE
 	  enables a live tree which is available after relocation,
 	  and can be adjusted as needed.
 
+config OF_UPSTREAM
+	bool "Enable use of devicetree imported from Linux kernel release"
+	help
+	  Traditionally, U-Boot platforms used to have their custom devicetree
+	  files or copy devicetree files from Linux kernel which are hard to
+	  maintain and can usually get out-of-sync from Linux kernel. This
+	  option enables platforms to migrate to devicetree-rebasing repo where
+	  a regular sync will be maintained every major Linux kernel release
+	  cycle. However, platforms can still have some custom u-boot specific
+	  bits maintained as part of *-u-boot.dtsi files.
+
+	  Note: This option should be set in Kconfig, for the SoC as a whole.
+	  However, newer boards whose devicetree source files haven't landed in
+	  the dts/upstream subtree, they can override this option to have the
+	  DT build from existing U-Boot tree location instead.
+
 choice
 	prompt "Provider of DTB for DT control"
 	depends on OF_CONTROL
diff --git a/dts/Makefile b/dts/Makefile
index 3437e54..d6c2c9d 100644
--- a/dts/Makefile
+++ b/dts/Makefile
@@ -10,10 +10,20 @@ ifeq ($(DEVICE_TREE),)
 DEVICE_TREE := unset
 endif
 
+ifeq ($(CONFIG_OF_UPSTREAM),y)
+ifeq ($(CONFIG_ARM64),y)
+dt_dir := dts/upstream/src/arm64
+else
+dt_dir := dts/upstream/src/$(ARCH)
+endif
+else
+dt_dir := arch/$(ARCH)/dts
+endif
+
 ifneq ($(EXT_DTB),)
 DTB := $(EXT_DTB)
 else
-DTB := arch/$(ARCH)/dts/$(DEVICE_TREE).dtb
+DTB := $(dt_dir)/$(DEVICE_TREE).dtb
 endif
 
 $(obj)/dt-$(SPL_NAME).dtb: dts/dt.dtb $(objtree)/tools/fdtgrep FORCE
@@ -41,7 +51,7 @@ $(DTB): arch-dtbs
 
 PHONY += arch-dtbs
 arch-dtbs:
-	$(Q)$(MAKE) $(build)=arch/$(ARCH)/dts dtbs
+	$(Q)$(MAKE) $(build)=$(dt_dir) dtbs
 
 ifeq ($(CONFIG_SPL_BUILD),y)
 obj-$(CONFIG_OF_EMBED) := dt-spl.dtb.o
@@ -65,4 +75,5 @@ clean-files := dt.dtb.S
 # Let clean descend into dts directories
 subdir- += ../arch/arc/dts ../arch/arm/dts ../arch/m68k/dts ../arch/microblaze/dts	\
 	   ../arch/mips/dts ../arch/nios2/dts ../arch/powerpc/dts ../arch/riscv/dts	\
-	   ../arch/sandbox/dts ../arch/sh/dts ../arch/x86/dts ../arch/xtensa/dts
+	   ../arch/sandbox/dts ../arch/sh/dts ../arch/x86/dts ../arch/xtensa/dts	\
+	   ./upstream/src/arm64 ./upstream/src/$(ARCH)
diff --git a/dts/upstream/src/arm64/Makefile b/dts/upstream/src/arm64/Makefile
new file mode 100644
index 0000000..9a8f6aa
--- /dev/null
+++ b/dts/upstream/src/arm64/Makefile
@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: GPL-2.0+
+
+include $(srctree)/scripts/Makefile.dts
+
+targets += $(dtb-y)
+
+# Add any required device tree compiler flags here
+DTC_FLAGS += -a 0x8
+
+PHONY += dtbs
+dtbs: $(addprefix $(obj)/, $(dtb-y))
+	@:
+
+clean-files := */*.dtb */*.dtbo