dts, kbuild: Implement support for dtb vendor subdirs

This patch adds support of vendor sub directories for dtb files.
Subdirectories can be specified in $(dts-dirs). Kbuild traverses over
all directories while building and installing dtb files. The directory
tree is also reflected in the install path.
Tested-by: Andrew Bresticker <abrestic@chromium.org>
Signed-off-by: Robert Richter <rrichter@cavium.com>

arch/arm64/boot/dts/Makefile

@@ -3,4 +3,5 @@ dtb-$(CONFIG_ARCH_VEXPRESS) += rtsm_ve-aemv8a.dtb foundation-v8.dtb
 dtb-$(CONFIG_ARCH_XGENE) += apm-mustang.dtb
 
 always		:= $(dtb-y)
+subdir-y	:= $(dts-dirs)
 clean-files	:= *.dtb

scripts/Makefile.dtbinst

@@ -6,6 +6,7 @@
 #
 #   $INSTALL_PATH/dtbs/$KERNELRELEASE
 #
+# Traverse through subdirectories listed in $(dts-dirs).
 # ==========================================================================
 
 src := $(obj)
@@ -13,26 +14,38 @@ src := $(obj)
 PHONY := __dtbs_install
 __dtbs_install:
 
+export dtbinst-root ?= $(obj)
+
 include include/config/auto.conf
 include scripts/Kbuild.include
 include $(srctree)/$(obj)/Makefile
 
 PHONY += __dtbs_install_prep
 __dtbs_install_prep:
+ifeq ("$(dtbinst-root)", "$(obj)")
 	$(Q)if [ -d $(INSTALL_DTBS_PATH).old ]; then rm -rf $(INSTALL_DTBS_PATH).old; fi
 	$(Q)if [ -d $(INSTALL_DTBS_PATH) ]; then mv $(INSTALL_DTBS_PATH) $(INSTALL_DTBS_PATH).old; fi
 	$(Q)mkdir -p $(INSTALL_DTBS_PATH)
+endif
 
 dtbinst-files	:= $(dtb-y)
+dtbinst-dirs	:= $(dts-dirs)
 
 # Helper targets for Installing DTBs into the boot directory
 quiet_cmd_dtb_install =	INSTALL $<
-      cmd_dtb_install =	cp $< $(2)
+      cmd_dtb_install =	mkdir -p $(2); cp $< $(2)
+
+install-dir = $(patsubst $(dtbinst-root)%,$(INSTALL_DTBS_PATH)%,$(obj))
+
+$(dtbinst-files) $(dtbinst-dirs): | __dtbs_install_prep
+
+$(dtbinst-files): %.dtb: $(obj)/%.dtb
+	$(call cmd,dtb_install,$(install-dir))
 
-$(dtbinst-files): %.dtb: $(obj)/%.dtb | __dtbs_install_prep
-	$(call cmd,dtb_install,$(INSTALL_DTBS_PATH))
+$(dtbinst-dirs):
+	$(Q)$(MAKE) $(dtbinst)=$(obj)/$@
 
-PHONY += $(dtbinst-files)
-__dtbs_install: $(dtbinst-files)
+PHONY += $(dtbinst-files) $(dtbinst-dirs)
+__dtbs_install: $(dtbinst-files) $(dtbinst-dirs)
 
 .PHONY: $(PHONY)