make.conf: Add the possibility to use another DTC

Add a make.conf DTC variable that control which DTC (Device Tree Compiler)
to use.

Reviewed by:	bdrewery, imp
Differential Revision:	https://reviews.freebsd.org/D9577

share/man/man5/make.conf.5

@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd March 29, 2016
+.Dd February 23, 2017
 .Dt MAKE.CONF 5
 .Os
 .Sh NAME
@@ -176,6 +176,11 @@ value, use
 .Dq Li +=
 instead of
 .Dq Li = .
+.It Va DTC
+.Pq Vt str
+Select the compiler for DTS (Device Tree Syntax) file.
+.Va DTC
+is initially set to the value of dtc
 .It Va INSTALL
 .Pq Vt str
 the default install command.

sys/conf/dtb.mk

@@ -4,6 +4,8 @@
 #
 # +++ variables +++
 #
+# DTC		The Device Tree Compiler to use
+#
 # DTS		List of the dts files to build and install.
 #
 # DTBDIR	Base path for dtb modules [/boot/dtb]
@@ -31,6 +33,8 @@
 # do this after bsd.own.mk.
 .include "kern.opts.mk"
 
+DTC?=		dtc
+
 # Search for kernel source tree in standard places.
 .for _dir in ${.CURDIR}/../.. ${.CURDIR}/../../.. /sys /usr/src/sys
 .if !defined(SYSDIR) && exists(${_dir}/kern/)
@@ -50,6 +54,7 @@ DTB=${DTS:R:S/$/.dtb/}
 all: ${DTB}
 
 .if defined(DTS)
+.export DTC
 .for _dts in ${DTS}
 ${_dts:R:S/$/.dtb/}:	${_dts} ${OP_META}
 	@echo Generating ${.TARGET} from ${_dts}

sys/tools/fdt/make_dtb.sh

@@ -16,9 +16,11 @@ if [ -z "${MACHINE}" ]; then
     MACHINE=$(uname -m)
 fi
 
+: ${DTC:=dtc}
+
 for d in ${dts}; do
     dtb=${dtb_path}/`basename $d .dts`.dtb
     echo "converting $d -> $dtb"
     cpp -P -x assembler-with-cpp -I $S/gnu/dts/include -I $S/boot/fdt/dts/${MACHINE} -I $S/gnu/dts/${MACHINE} -include $d /dev/null | 
-	dtc -@ -O dtb -o $dtb -b 0 -p 1024 -i $S/boot/fdt/dts/${MACHINE} -i $S/gnu/dts/${MACHINE}
+	${DTC} -@ -O dtb -o $dtb -b 0 -p 1024 -i $S/boot/fdt/dts/${MACHINE} -i $S/gnu/dts/${MACHINE}
 done