[RFC PATCH] 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.

Adding the dts subdirectory is straight-forward, but building the
DTBs should only happen for certain targets (dtbs, dtbs_check, %.dtb,
%.dtbo, and the directory target(s)).

The 'scripts_dtc' rule doesn't really depend on 'dt_binding_schemas',
but the directory target only depends on 'scripts' which depends on
'scripts_dtc'.

Signed-off-by: Rob Herring (Arm) <robh at kernel.org>
---
RFC because only arm64 converted ATM.

I don't really like looking at MAKECMDGOALS, but that's the only way I
could come up with that works. Maybe someone knows a better way.
---
 Makefile              | 2 +-
 arch/arm64/Kbuild     | 2 ++
 scripts/Makefile.dtbs | 3 +++
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 17cfa11ca716..85018d461575 100644
--- a/Makefile
+++ b/Makefile
@@ -1494,7 +1494,7 @@ export CHECK_DTBS=y
 endif
 
 ifneq ($(CHECK_DTBS),)
-dtbs_prepare: dt_binding_schemas
+scripts_dtc: dt_binding_schemas
 endif
 
 dtbs_check: dtbs
diff --git a/arch/arm64/Kbuild b/arch/arm64/Kbuild
index 5bfbf7d79c99..9e9820af48c9 100644
--- a/arch/arm64/Kbuild
+++ b/arch/arm64/Kbuild
@@ -5,5 +5,7 @@ obj-$(CONFIG_XEN)	+= xen/
 obj-$(subst m,y,$(CONFIG_HYPERV))	+= hyperv/
 obj-$(CONFIG_CRYPTO)	+= crypto/
 
+subdir-y += boot/dts
+
 # for cleaning
 subdir- += boot
diff --git a/scripts/Makefile.dtbs b/scripts/Makefile.dtbs
index 2d321b813600..4d0d164df275 100644
--- a/scripts/Makefile.dtbs
+++ b/scripts/Makefile.dtbs
@@ -14,7 +14,10 @@ dtb-y           := $(addprefix $(obj)/, $(dtb-y))
 multi-dtb-y     := $(addprefix $(obj)/, $(multi-dtb-y))
 real-dtb-y      := $(addprefix $(obj)/, $(real-dtb-y))
 
+ifneq ($(findstring /dts/,$(MAKECMDGOALS))$(findstring dtb,$(MAKECMDGOALS)),)
 always-y        += $(dtb-y)
+endif
+
 targets         += $(real-dtb-y)
 
 # dtbs-list
-- 
2.51.0