[BUILD] Generate include/autoconf.mk from board config files

Use cpp and sed to postprocess config.h and import the defined values
into include/autoconf.mk.  autoconf.mk is then included by config.mk to
give 'make' access to the board configuration.

Doing this enables conditional compilation at the Makefile level instead
of by wrapping every .c file with #ifdef/#endif wrappers.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

Makefile

@@ -342,6 +342,21 @@ $(obj)System.map:	$(obj)u-boot
 		grep -v '\(compiled\)\|\(\.o$$\)\|\( [aUw] \)\|\(\.\.ng$$\)\|\(LASH[RL]DI\)' | \
 		sort > $(obj)System.map
 
+#
+# Auto-generate the autoconf.mk file (which is included by all makefiles)
+#
+# This target actually generates 2 files; autoconf.mk and autoconf.mk.dep.
+# the dep file is only include in this top level makefile to determine when
+# to regenerate the autoconf.mk file.
+$(OBJTREE)/include/autoconf.mk: $(obj)include/config.h
+	@echo Generating include/autoconf.mk
+	@# Generate the dependancies
+	@$(CC) -M $(HOST_CFLAGS) $(CPPFLAGS) -MQ $@ include/common.h > $@.dep
+	@# Extract the config macros
+	@$(CPP) $(CFLAGS) -dM include/common.h | sed -n -f tools/scripts/define2mk.sed >> $@
+
+sinclude $(OBJTREE)/include/autoconf.mk.dep
+
 #########################################################################
 else
 all $(obj)u-boot.hex $(obj)u-boot.srec $(obj)u-boot.bin \
@@ -361,7 +376,8 @@ CHANGELOG:
 
 unconfig:
 	@rm -f $(obj)include/config.h $(obj)include/config.mk \
-		$(obj)board/*/config.tmp $(obj)board/*/*/config.tmp
+		$(obj)board/*/config.tmp $(obj)board/*/*/config.tmp \
+		$(obj)include/autoconf.mk $(obj)include/autoconf.mk.dep
 
 #========================================================================
 # PowerPC

config.mk

@@ -87,6 +87,9 @@ ifdef	BOARD
 sinclude $(TOPDIR)/board/$(BOARDDIR)/config.mk	# include board specific rules
 endif
 
+# Load generated board configuration
+sinclude $(OBJTREE)/include/autoconf.mk
+
 #########################################################################
 
 CONFIG_SHELL	:= $(shell if [ -x "$$BASH" ]; then echo $$BASH; \

tools/scripts/define2mk.sed

@@ -0,0 +1,29 @@
+#
+# Sed script to parse CPP macros and generate output usable by make
+#
+# It is expected that this script is fed the output of 'gpp -dM'
+# which preprocesses the common.h header files and outputs the final
+# list of CPP macros (and whitespace is sanitized)
+#
+
+# Only process values prefixed with #define CONFIG_
+/^#define CONFIG_[A-Za-z0-9_]\+/ {
+	# Strip the #define prefix
+	s/#define *//;
+	# Change to form CONFIG_*=VALUE
+	s/ \+/=/;
+	# Drop trailing spaces
+	s/ *$//;
+	# drop quotes around string values
+	s/="\(.*\)"$/=\1/;
+	# Concatenate string values
+	s/" *"//g;
+	# Wrap non-numeral values with quotes
+	s/=\(.*\?[^0-9].*\)$/=\"\1\"/;
+	# Change '1' and empty values to "y" (not perfect, but
+	# supports conditional compilation in the makefiles
+	s/=$/=y/;
+	s/=1$/=y/;
+	# print the line
+	p
+}