kbuild: simplify dtbs_install by reading the list of compiled DTBs

Retrieve the list of *.dtb(o) files from arch/*/boot/dts/dtbs-list
instead of traversing the directory tree again.

Please note that 'make dtbs_install' installs *.dtb(o) files directly
added to dtb-y because scripts/Makefile.dtbinst installs $(dtb-y)
without expanding the -dtbs suffix.

This commit preserves this behavior.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Makefile

@@ -1411,7 +1411,7 @@ endif
 dtbs_check: dtbs
 
 dtbs_install:
-	$(Q)$(MAKE) $(dtbinst)=$(dtstree) dst=$(INSTALL_DTBS_PATH)
+	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.dtbinst obj=$(dtstree)
 
 ifdef CONFIG_OF_EARLY_FLATTREE
 all: dtbs

scripts/Kbuild.include

@@ -113,12 +113,6 @@ endef
 # $(Q)$(MAKE) $(build)=dir
 build := -f $(srctree)/scripts/Makefile.build obj
 
-###
-# Shorthand for $(Q)$(MAKE) -f scripts/Makefile.dtbinst obj=
-# Usage:
-# $(Q)$(MAKE) $(dtbinst)=dir
-dtbinst := -f $(srctree)/scripts/Makefile.dtbinst obj
-
 ###
 # Shorthand for $(Q)$(MAKE) -f scripts/Makefile.clean obj=
 # Usage:

scripts/Makefile.dtbinst

@@ -8,32 +8,36 @@
 #   $INSTALL_PATH/dtbs/$KERNELRELEASE
 # ==========================================================================
 
-src := $(obj)
-
 PHONY := __dtbs_install
 __dtbs_install:
 
 include include/config/auto.conf
 include $(srctree)/scripts/Kbuild.include
-include $(kbuild-file)
-
-dtbs    := $(addprefix $(dst)/, $(dtb-y) $(if $(CONFIG_OF_ALL_DTBS),$(dtb-)))
-subdirs := $(addprefix $(obj)/, $(subdir-y) $(subdir-m))
 
-__dtbs_install: $(dtbs) $(subdirs)
-	@:
+dst := $(INSTALL_DTBS_PATH)
 
 quiet_cmd_dtb_install = INSTALL $@
       cmd_dtb_install = install -D $< $@
 
-$(dst)/%.dtb: $(obj)/%.dtb
+$(dst)/%: $(obj)/%
 	$(call cmd,dtb_install)
 
-$(dst)/%.dtbo: $(obj)/%.dtbo
-	$(call cmd,dtb_install)
+dtbs := $(patsubst $(obj)/%,%,$(call read-file, $(obj)/dtbs-list))
+
+ifdef CONFIG_ARCH_WANT_FLAT_DTB_INSTALL
 
-PHONY += $(subdirs)
-$(subdirs):
-	$(Q)$(MAKE) $(dtbinst)=$@ dst=$(if $(CONFIG_ARCH_WANT_FLAT_DTB_INSTALL),$(dst),$(patsubst $(obj)/%,$(dst)/%,$@))
+define gen_install_rules
+$(dst)/%: $(obj)/$(1)%
+	$$(call cmd,dtb_install)
+endef
+
+$(foreach d, $(sort $(dir $(dtbs))), $(eval $(call gen_install_rules,$(d))))
+
+dtbs := $(notdir $(dtbs))
+
+endif # CONFIG_ARCH_WANT_FLAT_DTB_INSTALL
+
+__dtbs_install: $(addprefix $(dst)/, $(dtbs))
+	@:
 
 .PHONY: $(PHONY)