[PATCH v3 0/2] kbuild: Support directory targets for DTBs

[PATCH v3 0/2] kbuild: Support directory targets for DTBs

[Rob Herring (Arm)]

This series adds support for using directory targets to build DTBs. This 
is primarily useful for architectures with lots of vendor DTS 
subdirectories.

v2 had some issues reported after I applied. In fixing David's issue,
that introduced random parallel build issues Arnd reported. I didn't get
it figured out quickly, so I ended up dropping it. I finally got
around to revisiting it with some LLM help this time. Having multiple 
paths in the build system to building DTBs complicates things, so I've 
reworked things to always use the single target and directory targets 
for building.

Arnd, can you give this a spin on your randconfig builds?
    
Please ack and I'll take this in the DT tree.

v3:
 - Convert %.dtbo? rules to single target
 - Convert dtbs rule to use directory target
 - Link to v2: https://lore.kernel.org/all/20251120204812.1983452-4-robh@kernel.org/

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
---
Rob Herring (Arm) (2):
      kbuild: Convert %.dtb(o) targets to single target rules
      kbuild: Support directory targets for building DTBs

 Makefile               | 32 ++++++++++++++++++++------------
 scripts/Makefile.build |  7 +++++++
 scripts/Makefile.dtbs  |  2 ++
 3 files changed, 29 insertions(+), 12 deletions(-)
---
base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
change-id: 20261007-dtb-dirs-v3-008fa5ffbc74

Best regards,
--  
Rob Herring (Arm) <robh@kernel.org>

[PATCH v3 1/2] kbuild: Convert %.dtb(o) targets to single target rules

[Rob Herring (Arm)]

Single .dtb and .dtbo targets can be built using the existing kbuild
single target infrastructure. The only difference is the custom rules
work on a relative path under the arch dts directory, so we have to
fixup the path for the single targets.

With this both relative and full paths work:

make arch/arm64/boot/dts/arm/juno.dtb
make arm/juno.dtb

Complicating matters is building DTBs works without $ARCH compiler as
only the host preprocessor is used. This is useful for building all the
DTBs in the tree without installing a bunch of cross-compilers. The
single target rule needs to depend on 'dtbs_prepare' rather the
'prepare' to maintain support for that.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
---
v3:
 - New patch
---
 Makefile | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/Makefile b/Makefile
index 4ad67b737af7..c307ee9293bc 100644
--- a/Makefile
+++ b/Makefile
@@ -301,7 +301,7 @@ no-dot-config-targets := $(clean-targets) \
 			 run-command
 no-sync-config-targets := $(no-dot-config-targets) %install modules_sign kernelrelease \
 			  image_name
-single-targets := %.a %.i %.ko %.lds %.ll %.lst %.mod %.o %.rsi %.s %/
+single-targets := %.a %.i %.ko %.lds %.ll %.lst %.mod %.o %.rsi %.s %.dtb %.dtbo %/
 
 config-build	:=
 mixed-build	:=
@@ -1663,12 +1663,6 @@ dtbindingtree := Documentation/devicetree/bindings
 
 ifneq ($(dtstree),)
 
-%.dtb: dtbs_prepare
-	$(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
-
-%.dtbo: dtbs_prepare
-	$(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
-
 PHONY += dtbs dtbs_prepare dtbs_install dtbs_check
 dtbs: dtbs_prepare
 	$(Q)$(MAKE) $(build)=$(dtstree) need-dtbslist=1
@@ -1683,7 +1677,7 @@ export CHECK_DTBS=y
 endif
 
 ifneq ($(CHECK_DTBS),)
-dtbs_prepare: dt_binding_schemas
+scripts_dtc: dt_binding_schemas
 endif
 
 dtbs_check: dtbs
@@ -2190,6 +2184,8 @@ modpost: $(if $(single-build),, $(if $(KBUILD_BUILTIN), vmlinux.o)) \
 #
 #   make foo/bar/baz/
 
+single-build-prep := prepare
+
 ifdef single-build
 
 # .ko is special because modpost is needed
@@ -2212,8 +2208,20 @@ ifneq ($(KBUILD_MODPOST_NOFINAL),1)
 endif
 	$(Q)rm -f modules.order
 
+# For compatibility with existing %.dtb targets without full path
+single-dtb := $(filter-out $(dtstree)/%, $(filter %.dtb %.dtbo, $(single-no-ko)))
+single-no-ko := $(filter-out $(single-dtb), $(single-no-ko)) $(addprefix $(dtstree)/, $(single-dtb))
+
 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 $(dtstree)/,%.dtb %.dtbo)
+ifeq ($(filter-out $(single-dt-patterns),$(single-no-ko)),)
+single-build-prep := dtbs_prepare
+endif
+endif
+
 KBUILD_MODULES := y
 
 endif
@@ -2225,7 +2233,7 @@ prepare: outputmakefile
 # make menuconfig etc.
 # Error messages still appears in the original language
 PHONY += $(build-dir)
-$(build-dir): prepare
+$(build-dir): $(single-build-prep)
 	$(Q)$(MAKE) $(build)=$@ need-builtin=1 need-modorder=1 $(single-goals)
 
 clean-dirs := $(addprefix _clean_, $(clean-dirs))

-- 
2.53.0

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

[Rob Herring (Arm)]

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

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

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] kbuild: unconditional need-dtbslist=1 causes unnecessary dtb compilation and dtbs-list files during standard builds
--

commit 645916678e1f6dbf830062f35ddde56a42d6b0df
Author: Rob Herring (Arm) <robh@kernel.org>

kbuild: Support directory targets for building DTBs

This commit modifies the Kbuild system to allow directory targets for
building all device tree binaries (DTBs) within a directory. It updates
both dtbs and single-build targets to use directory rules.

> diff --git a/Makefile b/Makefile
> index c307ee9293bcd..75d290c2b7d88 100644
> --- a/Makefile
> +++ b/Makefile
[ ... ]
> @@ -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)

[Severity: High]
Does adding need-dtbslist=1 unconditionally to the $(build-dir) recipe
cause unnecessary dtb compilation and empty dtbs-list file generation
during standard builds?

Because standard KBUILD_VMLINUX_OBJS targets (like built-in.a) depend
on '.' (which evaluates to $(build-dir)), 'make vmlinux' evaluates this
rule to recurse into the source tree. This exports need-dtbslist=1 into
MAKEFLAGS, which is then inherited by all Kbuild sub-makes.

> diff --git a/scripts/Makefile.dtbs b/scripts/Makefile.dtbs
> index c4e4663902844..c7ec2a2a308ef 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)

Because need-dtbslist=1 is globally inherited, it now unconditionally
appends all device trees to always-y in every visited directory.

Additionally, it triggers the generation of dtbs-list files across the
tree via existing code further down in scripts/Makefile.dtbs:

scripts/Makefile.dtbs:
    ifdef need-dtbslist
    subdir-dtbslist := $(addsuffix /dtbs-list, $(subdir-ym))
    dtb-y           += $(subdir-dtbslist)
    always-y        += $(obj)/dtbs-list
    endif

Could this unconditionally traverse arch/$(SRCARCH)/boot/dts/ and
compile all device trees, regressing build times, while cluttering
unrelated directories (like fs/ or mm/) with empty dtbs-list files?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261007-dtb-dirs-v3-v3-0-b3ab32b64fa6@kernel.org?part=2

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

[Rob Herring]

On Wed, Oct 07, 2026 at 01:39:41PM -0500, Rob Herring (Arm) wrote:
> 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)

sashiko points out that this creates dtblist files in every directory. 
Will make it conditional on having DTB targets.

Rob