Validate dtc is new enough

Subsequent patches assume that dtc supports various recent features.
These are available in dtc 1.4.0. Validate that dtc is at least that
version.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>

Makefile

@@ -413,7 +413,7 @@ endif
 
 all:		$(ALL-y) $(SUBDIR_EXAMPLES)
 
-$(obj)u-boot.dtb:	$(obj)u-boot
+$(obj)u-boot.dtb:	checkdtc $(obj)u-boot
 		$(MAKE) -C dts binary
 		mv $(obj)dts/dt.dtb $@
 
@@ -667,6 +667,12 @@ checkgcc4:
 		false; \
 	fi
 
+checkdtc:
+	@if test $(call dtc-version) -lt 0104; then \
+		echo '*** Your dtc is too old, please upgrade to dtc 1.4 or newer'; \
+		false; \
+	fi
+
 #
 # Auto-generate the autoconf.mk file (which is included by all makefiles)
 #

config.mk

@@ -119,6 +119,7 @@ endif
 # Usage gcc-ver := $(call cc-version)
 cc-version = $(shell $(SHELL) $(SRCTREE)/tools/gcc-version.sh $(CC))
 binutils-version = $(shell $(SHELL) $(SRCTREE)/tools/binutils-version.sh $(AS))
+dtc-version = $(shell $(SHELL) $(SRCTREE)/tools/dtc-version.sh $(DTC))
 
 #
 # Include the make variables (CC, etc...)

tools/dtc-version.sh

+#!/bin/sh
+#
+# dtc-version dtc-command
+#
+# Prints the dtc version of `dtc-command' in a canonical 4-digit form
+# such as `0222' for binutils 2.22
+#
+
+dtc="$*"
+
+if [ ${#dtc} -eq 0 ]; then
+	echo "Error: No dtc command specified."
+	printf "Usage:\n\t$0 <dtc-command>\n"
+	exit 1
+fi
+
+MAJOR=$($dtc -v | head -1 | awk '{print $NF}' | cut -d . -f 1)
+MINOR=$($dtc -v | head -1 | awk '{print $NF}' | cut -d . -f 2)
+
+printf "%02d%02d\\n" $MAJOR $MINOR