kbuild: verify dtoverlay files against schema

Currently only the single part device trees are validated against DT
schema. For the multipart DT files only the base DTB is validated.
Extend the fdtoverlay commands to validate the resulting DTB file
against schema.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20240527-dtbo-check-schema-v1-1-ee1094f88f74@linaro.org
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>

scripts/Makefile.lib

@@ -407,8 +407,15 @@ cmd_dtc = $(HOSTCC) -E $(dtc_cpp_flags) -x assembler-with-cpp -o $(dtc-tmp) $< ;
 		-d $(depfile).dtc.tmp $(dtc-tmp) ; \
 	cat $(depfile).pre.tmp $(depfile).dtc.tmp > $(depfile)
 
+DT_CHECK_CMD = $(DT_CHECKER) $(DT_CHECKER_FLAGS) -u $(srctree)/$(DT_BINDING_DIR) -p $(DT_TMP_SCHEMA)
+
+ifneq ($(CHECK_DTBS),)
+quiet_cmd_fdtoverlay = DTOVLCH $@
+      cmd_fdtoverlay = $(objtree)/scripts/dtc/fdtoverlay -o $@ -i $(real-prereqs) ; $(DT_CHECK_CMD) $@ || true
+else
 quiet_cmd_fdtoverlay = DTOVL   $@
       cmd_fdtoverlay = $(objtree)/scripts/dtc/fdtoverlay -o $@ -i $(real-prereqs)
+endif
 
 $(multi-dtb-y): FORCE
 	$(call if_changed,fdtoverlay)
@@ -421,7 +428,7 @@ DT_BINDING_DIR := Documentation/devicetree/bindings
 DT_TMP_SCHEMA := $(objtree)/$(DT_BINDING_DIR)/processed-schema.json
 
 quiet_cmd_dtb =	DTC_CHK $@
-      cmd_dtb =	$(cmd_dtc) ; $(DT_CHECKER) $(DT_CHECKER_FLAGS) -u $(srctree)/$(DT_BINDING_DIR) -p $(DT_TMP_SCHEMA) $@ || true
+      cmd_dtb =	$(cmd_dtc) ; $(DT_CHECK_CMD) $@ || true
 else
 quiet_cmd_dtb = $(quiet_cmd_dtc)
       cmd_dtb = $(cmd_dtc)