Devicetree build consolidation

Align powerpc with other architectures which build the dtb files in the same directory as the dts files. This is also in line with most other build targets which are located in the same directory as the source. This move will help enable the 'dtbs' target which builds all the dtbs regardless of kernel config.

This transition could break some scripts if they expect dtb files in the old location.

Cc Benjamin Herrenschmidt <[email protected]>

Cc Paul Mackerras <[email protected]>

Cc Michael Ellerman <[email protected]>

Cc [email protected]

Signed-off-by Rob Herring <[email protected]>

---
v3:
- Remove duplicate mpc5200 dtbs from image-y targets. The dtb target already comes from the cuImage.<platform> target.

 arch/powerpc/Makefile          |  2 +-
 arch/powerpc/boot/Makefile     | 55 ++++++++++++++++------------------
 arch/powerpc/boot/dts/Makefile |  1 +
 3 files changed, 28 insertions(+), 30 deletions(-)
 create mode 100644 arch/powerpc/boot/dts/Makefile

arch/powerpc/Makefile +1 -1

index 11a1acba164a..53ea887eb34e 100644
@@ -294,7 +294,7 @@ bootwrapper_install:
        $(Q)$(MAKE) $(build)=$(boot) $(patsubst %,$(boot)/%,$@)
 
 %.dtb: scripts
-       $(Q)$(MAKE) $(build)=$(boot) $(patsubst %,$(boot)/%,$@)
+       $(Q)$(MAKE) $(build)=$(boot)/dts $(patsubst %,$(boot)/dts/%,$@)
 
 # Used to create 'merged defconfigs'
 # To use it $(call) it with the first argument as the base defconfig

arch/powerpc/boot/Makefile +26 -29

index 0fb96c26136f..bca5c23767df 100644
@@ -304,9 +304,9 @@ image-$(CONFIG_PPC_ADDER875)                += cuImage.adder875-uboot \
                                           dtbImage.adder875-redboot
 
 # Board ports in arch/powerpc/platform/52xx/Kconfig
-image-$(CONFIG_PPC_LITE5200)           += cuImage.lite5200 lite5200.dtb
-image-$(CONFIG_PPC_LITE5200)           += cuImage.lite5200b lite5200b.dtb
-image-$(CONFIG_PPC_MEDIA5200)          += cuImage.media5200 media5200.dtb
+image-$(CONFIG_PPC_LITE5200)           += cuImage.lite5200
+image-$(CONFIG_PPC_LITE5200)           += cuImage.lite5200b
+image-$(CONFIG_PPC_MEDIA5200)          += cuImage.media5200
 
 # Board ports in arch/powerpc/platform/82xx/Kconfig
 image-$(CONFIG_MPC8272_ADS)            += cuImage.mpc8272ads

@@ -381,11 +381,11 @@ $(addprefix $(obj)/, $(sort $(filter zImage.%, $(image-y)))): vmlinux $(wrapperb
        $(call if_changed,wrap,$(subst $(obj)/zImage.,,$@))
 
 # dtbImage% - a dtbImage is a zImage with an embedded device tree blob
-$(obj)/dtbImage.initrd.%: vmlinux $(wrapperbits) $(obj)/%.dtb FORCE
-       $(call if_changed,wrap,$*,,$(obj)/$*.dtb,$(obj)/ramdisk.image.gz)
+$(obj)/dtbImage.initrd.%: vmlinux $(wrapperbits) $(obj)/dts/%.dtb FORCE
+       $(call if_changed,wrap,$*,,$(obj)/dts/$*.dtb,$(obj)/ramdisk.image.gz)
 
-$(obj)/dtbImage.%: vmlinux $(wrapperbits) $(obj)/%.dtb FORCE
-       $(call if_changed,wrap,$*,,$(obj)/$*.dtb)
+$(obj)/dtbImage.%: vmlinux $(wrapperbits) $(obj)/dts/%.dtb FORCE
+       $(call if_changed,wrap,$*,,$(obj)/dts/$*.dtb)
 
 # This cannot be in the root of $(src) as the zImage rule always adds a $(obj)
 # prefix

@@ -395,36 +395,33 @@ $(obj)/vmlinux.strip: vmlinux
 $(obj)/uImage: vmlinux $(wrapperbits) FORCE
        $(call if_changed,wrap,uboot)
 
-$(obj)/uImage.initrd.%: vmlinux $(obj)/%.dtb $(wrapperbits) FORCE
-       $(call if_changed,wrap,uboot-$*,,$(obj)/$*.dtb,$(obj)/ramdisk.image.gz)
+$(obj)/uImage.initrd.%: vmlinux $(obj)/dts/%.dtb $(wrapperbits) FORCE
+       $(call if_changed,wrap,uboot-$*,,$(obj)/dts/$*.dtb,$(obj)/ramdisk.image.gz)
 
-$(obj)/uImage.%: vmlinux $(obj)/%.dtb $(wrapperbits) FORCE
-       $(call if_changed,wrap,uboot-$*,,$(obj)/$*.dtb)
+$(obj)/uImage.%: vmlinux $(obj)/dts/%.dtb $(wrapperbits) FORCE
+       $(call if_changed,wrap,uboot-$*,,$(obj)/dts/$*.dtb)
 
-$(obj)/cuImage.initrd.%: vmlinux $(obj)/%.dtb $(wrapperbits) FORCE
-       $(call if_changed,wrap,cuboot-$*,,$(obj)/$*.dtb,$(obj)/ramdisk.image.gz)
+$(obj)/cuImage.initrd.%: vmlinux $(obj)/dts/%.dtb $(wrapperbits) FORCE
+       $(call if_changed,wrap,cuboot-$*,,$(obj)/dts/$*.dtb,$(obj)/ramdisk.image.gz)
 
-$(obj)/cuImage.%: vmlinux $(obj)/%.dtb $(wrapperbits) FORCE
-       $(call if_changed,wrap,cuboot-$*,,$(obj)/$*.dtb)
+$(obj)/cuImage.%: vmlinux $(obj)/dts/%.dtb $(wrapperbits) FORCE
+       $(call if_changed,wrap,cuboot-$*,,$(obj)/dts/$*.dtb)
 
-$(obj)/simpleImage.initrd.%: vmlinux $(obj)/%.dtb $(wrapperbits) FORCE
-       $(call if_changed,wrap,simpleboot-$*,,$(obj)/$*.dtb,$(obj)/ramdisk.image.gz)
+$(obj)/simpleImage.initrd.%: vmlinux $(obj)/dts/%.dtb $(wrapperbits) FORCE
+       $(call if_changed,wrap,simpleboot-$*,,$(obj)/dts/$*.dtb,$(obj)/ramdisk.image.gz)
 
-$(obj)/simpleImage.%: vmlinux $(obj)/%.dtb $(wrapperbits) FORCE
-       $(call if_changed,wrap,simpleboot-$*,,$(obj)/$*.dtb)
+$(obj)/simpleImage.%: vmlinux $(obj)/dts/%.dtb $(wrapperbits) FORCE
+       $(call if_changed,wrap,simpleboot-$*,,$(obj)/dts/$*.dtb)
 
-$(obj)/treeImage.initrd.%: vmlinux $(obj)/%.dtb $(wrapperbits) FORCE
-       $(call if_changed,wrap,treeboot-$*,,$(obj)/$*.dtb,$(obj)/ramdisk.image.gz)
+$(obj)/treeImage.initrd.%: vmlinux $(obj)/dts/%.dtb $(wrapperbits) FORCE
+       $(call if_changed,wrap,treeboot-$*,,$(obj)/dts/$*.dtb,$(obj)/ramdisk.image.gz)
 
-$(obj)/treeImage.%: vmlinux $(obj)/%.dtb $(wrapperbits) FORCE
-       $(call if_changed,wrap,treeboot-$*,,$(obj)/$*.dtb)
+$(obj)/treeImage.%: vmlinux $(obj)/dts/%.dtb $(wrapperbits) FORCE
+       $(call if_changed,wrap,treeboot-$*,,$(obj)/dts/$*.dtb)
 
-# Rule to build device tree blobs
-$(obj)/%.dtb: $(src)/dts/%.dts FORCE
-       $(call if_changed_dep,dtc)
-
-$(obj)/%.dtb: $(src)/dts/fsl/%.dts FORCE
-       $(call if_changed_dep,dtc)
+# Needed for the above targets to work with dts/fsl/ files
+$(obj)/dts/%.dtb: $(obj)/dts/fsl/%.dtb
+       @cp $< $@
 
 # If there isn't a platform selected then just strip the vmlinux.
 ifeq (,$(image-y))

arch/powerpc/boot/dts/Makefile new file +1 -1

new file mode 100644
index 000000000000..f66554cd5c45
@@ -0,0 +1 @@
+# SPDX-License-Identifier: GPL-2.0
--

2.17.1

There is nothing arch specific about building dtb files other than their location under /arch/*/boot/dts/. Keeping each arch aligned is a pain. The dependencies and supported targets are all slightly different. Also, a cross-compiler for each arch is needed, but really the host compiler preprocessor is perfectly fine for building dtbs. Move the build rules to a common location and remove the arch specific ones. This is done in a single step to avoid warnings about overriding rules.

The build dependencies had been a mixture of 'scripts' and/or 'prepare'. These pull in several dependencies some of which need a target compiler (specifically devicetable-offsets.h) and aren't needed to build dtbs. All that is really needed is dtc, so adjust the dependencies to only be dtc.

This change enables support 'dtbs_install' on some arches which were missing the target.

Makefile +14 -0

+
+%.dtb : scripts_dtc
+       $(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
+
+PHONY += dtbs dtbs_install
+dtbs: scripts_dtc
+       $(Q)$(MAKE) $(build)=$(dtstree)
+
+dtbs_install: dtbs
+       $(Q)$(MAKE) $(dtbinst)=$(dtstree)
+
+all: dtbs
+
+endif

Quoted 17 lines

There is nothing arch specific about building dtb files other than their location under /arch/*/boot/dts/. Keeping each arch aligned is a pain. The dependencies and supported targets are all slightly different. Also, a cross-compiler for each arch is needed, but really the host compiler preprocessor is perfectly fine for building dtbs. Move the build rules to a common location and remove the arch specific ones. This is done in a single step to avoid warnings about overriding rules.

The build dependencies had been a mixture of 'scripts' and/or 'prepare'. These pull in several dependencies some of which need a target compiler (specifically devicetable-offsets.h) and aren't needed to build dtbs. All that is really needed is dtc, so adjust the dependencies to only be dtc.

This change enables support 'dtbs_install' on some arches which were missing the target.

[...]

Makefile kselftest-merge: · line 1225

Quoted 12 lines

Makefile +8 -0

@@ -1215,6 +1215,33 @@ kselftest-merge:
                $(srctree)/tools/testing/selftests/*/config
        +$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig
 
+# ---------------------------------------------------------------------------
+# Devicetree files
+
+ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/boot/dts/),)
+dtstree := arch/$(SRCARCH)/boot/dts
+endif
+
+ifdef CONFIG_OF_EARLY_FLATTREE

This can be true when dtstree is unset. So this line should be this instead to fix the 0-day reported error:

ifneq ($(dtstree),)

Quoted 4 lines

Makefile +4 -0

+
+%.dtb : scripts_dtc
+       $(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
+

Makefile kselftest-merge: · line 1239

Quoted 10 lines

Makefile +10 -0

+PHONY += dtbs dtbs_install
+dtbs: scripts_dtc
+       $(Q)$(MAKE) $(build)=$(dtstree)
+
+dtbs_install: dtbs
+       $(Q)$(MAKE) $(dtbinst)=$(dtstree)
+
+all: dtbs
+
+endif

2018-09-12 0:40 GMT+09:00 Rob Herring <[email protected]>:

Quoted 38 lines · Rob Herring

Quoted 16 lines

There is nothing arch specific about building dtb files other than their location under /arch/*/boot/dts/. Keeping each arch aligned is a pain. The dependencies and supported targets are all slightly different. Also, a cross-compiler for each arch is needed, but really the host compiler preprocessor is perfectly fine for building dtbs. Move the build rules to a common location and remove the arch specific ones. This is done in a single step to avoid warnings about overriding rules.

The build dependencies had been a mixture of 'scripts' and/or 'prepare'. These pull in several dependencies some of which need a target compiler (specifically devicetable-offsets.h) and aren't needed to build dtbs. All that is really needed is dtc, so adjust the dependencies to only be dtc.

This change enables support 'dtbs_install' on some arches which were missing the target.

[...]

Makefile kselftest-merge: · line 1225

Quoted 12 lines

Makefile +8 -0

@@ -1215,6 +1215,33 @@ kselftest-merge:
                $(srctree)/tools/testing/selftests/*/config
        +$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig
 
+# ---------------------------------------------------------------------------
+# Devicetree files
+
+ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/boot/dts/),)
+dtstree := arch/$(SRCARCH)/boot/dts
+endif
+
+ifdef CONFIG_OF_EARLY_FLATTREE

This can be true when dtstree is unset. So this line should be this instead to fix the 0-day reported error:

ifneq ($(dtstree),)

Quoted 14 lines

Quoted 4 lines

Makefile +4 -0

+
+%.dtb : scripts_dtc
+       $(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
+

Makefile kselftest-merge: · line 1239

Quoted 10 lines

Makefile +10 -0

+PHONY += dtbs dtbs_install
+dtbs: scripts_dtc
+       $(Q)$(MAKE) $(build)=$(dtstree)
+
+dtbs_install: dtbs
+       $(Q)$(MAKE) $(dtbinst)=$(dtstree)
+
+all: dtbs
+
+endif

Ah, right.
Even x86 can enable OF and OF_UNITTEST.

Another solution might be,
guard it by 'depends on ARCH_SUPPORTS_OF'.

This is actually what ACPI does.

menuconfig ACPI
bool "ACPI (Advanced Configuration and Power Interface) Support" depends on ARCH_SUPPORTS_ACPI
...

Hi Yamada-san,

Quoted 65 lines · Masahiro Yamada

2018-09-12 0:40 GMT+09:00 Rob Herring <[email protected]>:

Quoted 38 lines · Rob Herring

Quoted 16 lines

There is nothing arch specific about building dtb files other than their location under /arch/*/boot/dts/. Keeping each arch aligned is a pain. The dependencies and supported targets are all slightly different. Also, a cross-compiler for each arch is needed, but really the host compiler preprocessor is perfectly fine for building dtbs. Move the build rules to a common location and remove the arch specific ones. This is done in a single step to avoid warnings about overriding rules.

The build dependencies had been a mixture of 'scripts' and/or 'prepare'. These pull in several dependencies some of which need a target compiler (specifically devicetable-offsets.h) and aren't needed to build dtbs. All that is really needed is dtc, so adjust the dependencies to only be dtc.

This change enables support 'dtbs_install' on some arches which were missing the target.

[...]

Makefile kselftest-merge: · line 1225

Quoted 12 lines

Makefile +8 -0

@@ -1215,6 +1215,33 @@ kselftest-merge:
                $(srctree)/tools/testing/selftests/*/config
        +$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig
 
+# ---------------------------------------------------------------------------
+# Devicetree files
+
+ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/boot/dts/),)
+dtstree := arch/$(SRCARCH)/boot/dts
+endif
+
+ifdef CONFIG_OF_EARLY_FLATTREE

This can be true when dtstree is unset. So this line should be this instead to fix the 0-day reported error:

ifneq ($(dtstree),)

Quoted 14 lines

Quoted 4 lines

Makefile +4 -0

+
+%.dtb : scripts_dtc
+       $(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
+

Makefile kselftest-merge: · line 1239

Quoted 10 lines

Makefile +10 -0

+PHONY += dtbs dtbs_install
+dtbs: scripts_dtc
+       $(Q)$(MAKE) $(build)=$(dtstree)
+
+dtbs_install: dtbs
+       $(Q)$(MAKE) $(dtbinst)=$(dtstree)
+
+all: dtbs
+
+endif

Ah, right.
Even x86 can enable OF and OF_UNITTEST.

Another solution might be,
guard it by 'depends on ARCH_SUPPORTS_OF'.

Quoted 6 lines

This is actually what ACPI does.

menuconfig ACPI
bool "ACPI (Advanced Configuration and Power Interface) Support" depends on ARCH_SUPPORTS_ACPI
...

ACPI is a real platform feature, as it depends on firmware.

CONFIG_OF can be enabled, and DT overlays can be loaded, on any platform, even if it has ACPI ;-)

2018-09-13 11:51 GMT-04:00 Geert Uytterhoeven <[email protected]>:

Quoted 76 lines

Hi Yamada-san,

Quoted 71 lines · Masahiro Yamada

2018-09-12 0:40 GMT+09:00 Rob Herring <[email protected]>:

Quoted 38 lines · Rob Herring

Quoted 16 lines

There is nothing arch specific about building dtb files other than their location under /arch/*/boot/dts/. Keeping each arch aligned is a pain. The dependencies and supported targets are all slightly different. Also, a cross-compiler for each arch is needed, but really the host compiler preprocessor is perfectly fine for building dtbs. Move the build rules to a common location and remove the arch specific ones. This is done in a single step to avoid warnings about overriding rules.

The build dependencies had been a mixture of 'scripts' and/or 'prepare'. These pull in several dependencies some of which need a target compiler (specifically devicetable-offsets.h) and aren't needed to build dtbs. All that is really needed is dtc, so adjust the dependencies to only be dtc.

This change enables support 'dtbs_install' on some arches which were missing the target.

[...]

Makefile kselftest-merge: · line 1225

Quoted 12 lines

Makefile +8 -0

@@ -1215,6 +1215,33 @@ kselftest-merge:
                $(srctree)/tools/testing/selftests/*/config
        +$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig
 
+# ---------------------------------------------------------------------------
+# Devicetree files
+
+ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/boot/dts/),)
+dtstree := arch/$(SRCARCH)/boot/dts
+endif
+
+ifdef CONFIG_OF_EARLY_FLATTREE

This can be true when dtstree is unset. So this line should be this instead to fix the 0-day reported error:

ifneq ($(dtstree),)

Quoted 14 lines

Quoted 4 lines

Makefile +4 -0

+
+%.dtb : scripts_dtc
+       $(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
+

Makefile kselftest-merge: · line 1239

Quoted 10 lines

Makefile +10 -0

+PHONY += dtbs dtbs_install
+dtbs: scripts_dtc
+       $(Q)$(MAKE) $(build)=$(dtstree)
+
+dtbs_install: dtbs
+       $(Q)$(MAKE) $(dtbinst)=$(dtstree)
+
+all: dtbs
+
+endif

Ah, right.
Even x86 can enable OF and OF_UNITTEST.

Another solution might be,
guard it by 'depends on ARCH_SUPPORTS_OF'.

This is actually what ACPI does.

menuconfig ACPI
bool "ACPI (Advanced Configuration and Power Interface) Support" depends on ARCH_SUPPORTS_ACPI
...

Quoted 5 lines

ACPI is a real platform feature, as it depends on firmware.

CONFIG_OF can be enabled, and DT overlays can be loaded, on any platform, even if it has ACPI ;-)

OK, understood.

Makefile +12 -1

+       $(Q)$(MAKE) $(dtbinst)=$(dtstree)
+
+ifdef CONFIG_OF_EARLY_FLATTREE
+all: dtbs
+endif
+
+endif
+
+PHONY += scripts_dtc
+scripts_dtc: scripts_basic
+       $(Q)$(MAKE) $(build)=scripts/dtc
+
 #
---------------------------------------------------------------------------
 # Modules

Hi Rob,

2018?9?29?(?) 0:43 Rob Herring <[email protected]>:

Review

Quoted 11 lines

(quoted diff) +10 -1

+#
---------------------------------------------------------------------------
+# Devicetree files
+
+ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/boot/dts/),)
+dtstree := arch/$(SRCARCH)/boot/dts
+endif
+
+ifneq ($(dtstree),)
+
+%.dtb : scripts_dtc

%.dtb: prepare3 prepare

because we need to make sure KERNELRELEASE
is correctly defined before dtbs_install happens.

Review

Quoted 6 lines

(quoted diff) +4 -0

+       $(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
+
+PHONY += dtbs dtbs_install
+dtbs: scripts_dtc

dtbs: prepare3 scripts_dtc

Review

Quoted 3 lines

(quoted diff) +3 -0

+       $(Q)$(MAKE) $(build)=$(dtstree)
+
+dtbs_install: dtbs

Please do not have dtbs_install to depend on dtbs.

No install targets should ever trigger building anything in the source tree.

For the background, see the commit log of
19514fc665ffbce624785f76ee7ad0ea6378a527

Quoted 6 lines · Masahiro Yamada

Hi Rob,

2018?9?29?(?) 0:43 Rob Herring <[email protected]>:

Quoted 13 lines

Review

Quoted 11 lines

(quoted diff) +10 -1

+#
---------------------------------------------------------------------------
+# Devicetree files
+
+ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/boot/dts/),)
+dtstree := arch/$(SRCARCH)/boot/dts
+endif
+
+ifneq ($(dtstree),)
+
+%.dtb : scripts_dtc

%.dtb: prepare3 prepare

I assume you didn't mean to drop scripts_dtc as that doesn't work.

Why "prepare" here and not on dtbs?

Quoted 2 lines

because we need to make sure KERNELRELEASE
is correctly defined before dtbs_install happens.

Yes, indeed. With prepare3 added I get:

cp: cannot create regular file '/boot/dtbs/4.19.0-rc3-00009-g0afba9b7b2ea-dirty': No such file or directory

vs. with it:

cp: cannot create regular file '/boot/dtbs/': Not a directory

Quoted 19 lines

Review

Quoted 6 lines

(quoted diff) +4 -0

+       $(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
+
+PHONY += dtbs dtbs_install
+dtbs: scripts_dtc

dtbs: prepare3 scripts_dtc

Review

Quoted 3 lines

(quoted diff) +3 -0

+       $(Q)$(MAKE) $(build)=$(dtstree)
+
+dtbs_install: dtbs

Please do not have dtbs_install to depend on dtbs.

Quoted 6 lines

No install targets should ever trigger building anything in the source tree.

For the background, see the commit log of
19514fc665ffbce624785f76ee7ad0ea6378a527

Okay, thanks.

Rob

Quoted 11 lines · Masahiro Yamada

Even x86 can enable OF and OF_UNITTEST.

Another solution might be,
guard it by 'depends on ARCH_SUPPORTS_OF'.

This is actually what ACPI does.

menuconfig ACPI
bool "ACPI (Advanced Configuration and Power Interface) Support" depends on ARCH_SUPPORTS_ACPI
...

ACPI is a real platform feature, as it depends on firmware.

CONFIG_OF can be enabled, and DT overlays can be loaded, on any platform, even if it has ACPI ;-)

Hi Geert,

Am 13.09.18 um 17:51 schrieb Geert Uytterhoeven:

Quoted 14 lines

Quoted 11 lines · Masahiro Yamada

Even x86 can enable OF and OF_UNITTEST.

Another solution might be,
guard it by 'depends on ARCH_SUPPORTS_OF'.

This is actually what ACPI does.

menuconfig ACPI
bool "ACPI (Advanced Configuration and Power Interface) Support" depends on ARCH_SUPPORTS_ACPI
...

Quoted 4 lines

ACPI is a real platform feature, as it depends on firmware.

CONFIG_OF can be enabled, and DT overlays can be loaded, on any platform, even if it has ACPI ;-)

How would loading a DT overlay work on an ACPI platform? I.e., what would it overlay against and how to practically load such a file?

I wonder whether that could be helpful for USB devices and serdev...

Quoted 15 lines · Andreas F?rber

Am 13.09.18 um 17:51 schrieb Geert Uytterhoeven:

Quoted 14 lines

Quoted 11 lines · Masahiro Yamada

Even x86 can enable OF and OF_UNITTEST.

Another solution might be,
guard it by 'depends on ARCH_SUPPORTS_OF'.

This is actually what ACPI does.

menuconfig ACPI
bool "ACPI (Advanced Configuration and Power Interface) Support" depends on ARCH_SUPPORTS_ACPI
...

Quoted 7 lines

Quoted 4 lines

ACPI is a real platform feature, as it depends on firmware.

CONFIG_OF can be enabled, and DT overlays can be loaded, on any platform, even if it has ACPI ;-)

How would loading a DT overlay work on an ACPI platform? I.e., what would it overlay against and how to practically load such a file?

The DT unittests do just that. I run them on x86 and UM builds. In this case, the loading source is built-in.

Quoted 1 line

I wonder whether that could be helpful for USB devices and serdev...

How to load the overlays is pretty orthogonal to the issues to be solved here. It would certainly be possible to move forward with prototyping this and just have the overlay built-in. It may not even need to be an overlay if we can support multiple root nodes.