Index: sys/conf/Makefile.arm
===================================================================
--- sys/conf/Makefile.arm
+++ sys/conf/Makefile.arm
@@ -169,3 +169,4 @@
 %RULES
 	
 .include "$S/conf/kern.post.mk"
+.include "$S/conf/dtb.mk"
Index: sys/conf/Makefile.arm64
===================================================================
--- sys/conf/Makefile.arm64
+++ sys/conf/Makefile.arm64
@@ -46,3 +46,4 @@
 %RULES
 
 .include "$S/conf/kern.post.mk"
+.include "$S/conf/dtb.mk"
Index: sys/conf/dtb.mk
===================================================================
--- sys/conf/dtb.mk
+++ sys/conf/dtb.mk
@@ -49,35 +49,51 @@
 
 .PATH: ${SYSDIR}/gnu/dts/${MACHINE} ${SYSDIR}/dts/${MACHINE} ${SYSDIR}/dts/${MACHINE}/overlays
 
-DTB=${DTS:R:S/$/.dtb/}
-DTBO=${DTSO:R:S/$/.dtbo/}
-
-all: ${DTB} ${DTBO}
-
 .if defined(DTS)
-.export DTC ECHO
 .for _dts in ${DTS}
-${_dts:R:S/$/.dtb/}:	${_dts} ${OP_META}
-	@${ECHO} Generating ${.TARGET} from ${_dts}
-	@${SYSDIR}/tools/fdt/make_dtb.sh ${SYSDIR} ${_dts} ${.OBJDIR}
-CLEANFILES+=${_dts:R:S/$/.dtb/}
+_dtb=${_dts:T:R:S/$/.dtb/}
+.if !empty(DTS_${_dtb})
+.warning "Duplicated DTS ${_dts}"
+.endif
+
+DTB:=${DTB} ${_dtb}
+DTS_${_dtb}:=${_dts}
 .endfor
 .endif
 
 .if defined(DTSO)
-.export DTC ECHO
 .for _dtso in ${DTSO}
-${_dtso:R:S/$/.dtbo/}:	${_dtso} ${OP_META}
-	@${ECHO} Generating ${.TARGET} from ${_dtso}
-	@${SYSDIR}/tools/fdt/make_dtbo.sh ${SYSDIR} overlays/${_dtso} ${.OBJDIR}
-CLEANFILES+=${_dtso:R:S/$/.dtbo/}
+_dtso_path=${_dtso:C/^([^\/])/overlays\/\\1/}
+_dtbo=${_dtso:T:R:S/$/.dtbo/}
+.if !empty(DTSO_${_dtbo})
+.warning "Duplicated DTSO ${_dtso}"
+.endif
+
+DTBO:=${DTBO} ${_dtbo}
+DTSO_${_dtbo}:=${_dtso_path}
+.endfor
+.endif
+
+.if defined(DTB)
+.export DTC ECHO
+.for _dtb in ${DTB}
+${_dtb}:	${_dts} ${OP_META}
+	@${ECHO} Generating ${.TARGET} from ${DTS_${.TARGET}}
+	@${SYSDIR}/tools/fdt/make_dtb.sh ${SYSDIR} ${DTS_${.TARGET}} ${.OBJDIR}
+CLEANFILES+=${_dtb}
+.endfor
+.endif
+
+.if defined(DTBO)
+.export DTC ECHO
+.for _dtbo in ${DTBO}
+${_dtbo}:	${DTSO_${.TARGET}} ${OP_META}
+	@${ECHO} Generating ${.TARGET} from ${DTSO_${.TARGET}}
+	@${SYSDIR}/tools/fdt/make_dtbo.sh ${SYSDIR} ${DTSO_${.TARGET}} ${.OBJDIR}
+CLEANFILES+=${_dtbo}
 .endfor
 .endif
 
-.if !target(install)
-.if !target(realinstall)
-realinstall: _dtbinstall
-.ORDER: beforeinstall _kmodinstall
 _dtbinstall:
 # Need to create this because installkernel doesn't invoke mtree with BSD.root.mtree
 # to make sure the tree is setup properly. We don't recreate it to avoid duplicate
@@ -85,9 +101,13 @@
 	test -d ${DESTDIR}${DTBDIR} || ${INSTALL} -d -o ${DTBOWN} -g ${DTBGRP} ${DESTDIR}${DTBDIR}
 .for _dtb in ${DTB}
 .if ${MACHINE_CPUARCH} == "aarch64"
-	test -d ${DESTDIR}${DTBDIR}/${_dtb:H} || ${INSTALL} -d -o ${DTBOWN} -g ${DTBGRP} ${DESTDIR}${DTBDIR}/${_dtb:H}
+	# :H:T here to grab the vendor component of the DTB path in a way that
+	# allows out-of-tree DTS builds, too.  We make the assumption that
+	# out-of-tree DTS will have a similar directory structure to in-tree,
+	# with .dts files appearing in a vendor/ directory.
+	test -d ${DESTDIR}${DTBDIR}/${_dtb:H:T} || ${INSTALL} -d -o ${DTBOWN} -g ${DTBGRP} ${DESTDIR}${DTBDIR}/${_dtb:H:T}
 	${INSTALL} -o ${DTBOWN} -g ${DTBGRP} -m ${DTBMODE} \
-	    ${_INSTALLFLAGS} ${_dtb:T} ${DESTDIR}${DTBDIR}/${_dtb:H}
+	    ${_INSTALLFLAGS} ${_dtb:T} ${DESTDIR}${DTBDIR}/${_dtb:H:T}
 .else
 	${INSTALL} -o ${DTBOWN} -g ${DTBGRP} -m ${DTBMODE} \
 	    ${_INSTALLFLAGS} ${_dtb} ${DESTDIR}${DTBDIR}/
@@ -98,9 +118,16 @@
 	${INSTALL} -o ${DTBOWN} -g ${DTBGRP} -m ${DTBMODE} \
 	    ${_INSTALLFLAGS} ${_dtbo} ${DESTDIR}${DTBODIR}/
 .endfor
-.endif # !target(realinstall)
-.endif # !target(install)
 
-.include <bsd.dep.mk>
+.if target(kernel-install)
+kernel-all: ${DTB} ${DTBO}
+kernel-install: _dtbinstall
+.ORDER: beforeinstall _dtbinstall
+.elif !target(install) && !target(realinstall)
+all: ${DTB} ${DTBO}
+realinstall: _dtbinstall
+.ORDER: beforeinstall _dtbinstall
+
 .include <bsd.obj.mk>
 .include <bsd.links.mk>
+.endif # !target(install) && !target(realinstall)