[PATCH v3 2/2] kbuild: Support directory targets for building DTBs

["Rob Herring (Arm)" <robh@kernel.org>]

It is useful to be able to build all the DTBs for a vendor. One can list
all the .dts files in a directory and convert those to %.dtb targets,
but that doesn't work for base+overlay DTB targets.

The 'dtbs' and 'dtbs_check' targets can use the directory rule targets
as well which avoids different make paths for building DTBs.

Assisted-by: LLM
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
---
v3:
 - Reworked on top of single target rule for %.dtb
 - Make dtbs target use directory rule.
 - Move adding boot/dts subdir out of the arch code. Now supported on
   every arch (not that useful without vendor dirs).
 - Removed the need to look at MAKECMDGOALS
 - Fixed unnecessary rebuilding DT base+overlay targets
 - Link to v2: https://lore.kernel.org/all/20251120204812.1983452-4-robh@kernel.org/

v2:
 - Convert arm, mips and riscv. The other DT enabled arches don't have
   vendor directories.
 - Link to v1: https://lore.kernel.org/all/20251113225952.867138-1-robh@kernel.org/
---
 Makefile               | 8 ++++----
 scripts/Makefile.build | 7 +++++++
 scripts/Makefile.dtbs  | 2 ++
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/Makefile b/Makefile
index c307ee9293bc..75d290c2b7d8 100644
--- a/Makefile
+++ b/Makefile
@@ -1664,8 +1664,8 @@ dtbindingtree := Documentation/devicetree/bindings
 ifneq ($(dtstree),)
 
 PHONY += dtbs dtbs_prepare dtbs_install dtbs_check
-dtbs: dtbs_prepare
-	$(Q)$(MAKE) $(build)=$(dtstree) need-dtbslist=1
+dtbs:
+	$(Q)$(MAKE) $(dtstree)/
 
 # include/config/kernel.release is actually needed when installing DTBs because
 # INSTALL_DTBS_PATH contains $(KERNELRELEASE). However, we do not want to make
@@ -2216,7 +2216,7 @@ single-goals := $(addprefix $(build-dir)/, $(single-no-ko))
 
 # DT-only targets need host tools, but no architecture-specific preparation.
 ifneq ($(dtstree),)
-single-dt-patterns := $(addprefix $(dtstree)/,%.dtb %.dtbo)
+single-dt-patterns := $(dtstree)/ $(addprefix $(dtstree)/,%.dtb %.dtbo %/)
 ifeq ($(filter-out $(single-dt-patterns),$(single-no-ko)),)
 single-build-prep := dtbs_prepare
 endif
@@ -2234,7 +2234,7 @@ prepare: outputmakefile
 # Error messages still appears in the original language
 PHONY += $(build-dir)
 $(build-dir): $(single-build-prep)
-	$(Q)$(MAKE) $(build)=$@ need-builtin=1 need-modorder=1 $(single-goals)
+	$(Q)$(MAKE) $(build)=$@ need-builtin=1 need-modorder=1 need-dtbslist=1 $(single-goals)
 
 clean-dirs := $(addprefix _clean_, $(clean-dirs))
 PHONY += $(clean-dirs) clean
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 4349108e75e1..d22b3b2d43b3 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -38,6 +38,13 @@ include $(srctree)/scripts/Makefile.compiler
 include $(kbuild-file)
 include $(srctree)/scripts/Makefile.lib
 
+# Make DT directory targets reachable for architectures with a DTS tree.
+ifeq ($(obj),arch/$(SRCARCH))
+ifneq ($(wildcard $(src)/boot/dts/),)
+subdir-y += boot/dts
+endif
+endif
+
 # flags that take effect in current and sub directories
 KBUILD_AFLAGS += $(subdir-asflags-y)
 KBUILD_CFLAGS += $(subdir-ccflags-y)
diff --git a/scripts/Makefile.dtbs b/scripts/Makefile.dtbs
index c4e466390284..c7ec2a2a308e 100644
--- a/scripts/Makefile.dtbs
+++ b/scripts/Makefile.dtbs
@@ -23,7 +23,9 @@ dtb-y           := $(addprefix $(obj)/, $(dtb-y))
 multi-dtb-y     := $(addprefix $(obj)/, $(multi-dtb-y))
 real-dtb-y      := $(addprefix $(obj)/, $(real-dtb-y))
 
+ifdef need-dtbslist
 always-y        += $(dtb-y)
+endif
 targets         += $(real-dtb-y)
 
 # dtbs-list

-- 
2.53.0