[U-Boot] [PATCH v2] SPL: Makefile: Build a separate autoconf.mk for SPL

[Joel A Fernandes]

SPL defines CONFIG_SPL_BUILD but this does not percolate to the autoconf.mk Makefile.
As a result the build breaks when CONFIG_SPL_BUILD is used in the board-specific include
header file. With this, there is a possibility of having a CONFIG option defined in the
header file but not defined in the Makefile causing all kinds of build failure and problems.

It also messes things for up, for example, when one might want to undefine options to
keep the SPL small and doesn't want to be stuck with the CONFIG options used for U-boot.
Lastly, this also avoids defining special CONFIG_SPL_ variables for cases where some
options are required in U-boot but not in SPL.

We add a spl-autoconf.mk rule that is generated for SPL with the CONFIG_SPL_BUILD flag
and conditionally include it for SPL builds.

v2 changes:
Fixed issue where builds in a different directory were failing.
Suggested-by: Muddegowda, Deepak <x0171695 at ti.com> . Thanks Deepak!
Reported-by: Tom Rini <trini at ti.com>

Signed-off-by: Joel A Fernandes <joelagnel at ti.com>
Cc: Muddegowda, Deepak <x0171695 at ti.com>
Cc: Tom Rini <trini at ti.com>
---
 Makefile  |   19 +++++++++++++++++--
 config.mk |    6 ++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 6a30e04..e3a87e5 100644
--- a/Makefile
+++ b/Makefile
@@ -567,6 +567,7 @@ updater:
 # Explicitly make _depend in subdirs containing multiple targets to prevent
 # parallel sub-makes creating .depend files simultaneously.
 depend dep:	$(TIMESTAMP_FILE) $(VERSION_FILE) \
+		$(obj)include/spl-autoconf.mk \
 		$(obj)include/autoconf.mk \
 		$(obj)include/generated/generic-asm-offsets.h \
 		$(obj)include/generated/asm-offsets.h
@@ -632,12 +633,23 @@ $(obj)include/autoconf.mk: $(obj)include/config.h
 		sed -n -f tools/scripts/define2mk.sed > $@.tmp && \
 	mv $@.tmp $@
 
+# Auto-generate the spl-autoconf.mk file (which is included by all makefiles for SPL)
+$(obj)include/spl-autoconf.mk: $(obj)include/config.h
+	@$(XECHO) Generating $@ ; \
+	set -e ; \
+	: Extract the config macros ; \
+	$(CPP) $(CFLAGS) -DCONFIG_SPL_BUILD -DDO_DEPS_ONLY -dM include/common.h | \
+	sed -n -f tools/scripts/define2mk.sed > $@.tmp && \
+	mv $@.tmp $@
+
 $(obj)include/generated/generic-asm-offsets.h:	$(obj)include/autoconf.mk.dep \
+	$(obj)include/spl-autoconf.mk \
 	$(obj)lib/asm-offsets.s
 	@$(XECHO) Generating $@
 	tools/scripts/make-asm-offsets $(obj)lib/asm-offsets.s $@
 
 $(obj)lib/asm-offsets.s:	$(obj)include/autoconf.mk.dep \
+	$(obj)include/spl-autoconf.mk \
 	$(src)lib/asm-offsets.c
 	@mkdir -p $(obj)lib
 	$(CC) -DDO_DEPS_ONLY \
@@ -645,11 +657,13 @@ $(obj)lib/asm-offsets.s:	$(obj)include/autoconf.mk.dep \
 		-o $@ $(src)lib/asm-offsets.c -c -S
 
 $(obj)include/generated/asm-offsets.h:	$(obj)include/autoconf.mk.dep \
+	$(obj)include/spl-autoconf.mk \
 	$(obj)$(CPUDIR)/$(SOC)/asm-offsets.s
 	@$(XECHO) Generating $@
 	tools/scripts/make-asm-offsets $(obj)$(CPUDIR)/$(SOC)/asm-offsets.s $@
 
-$(obj)$(CPUDIR)/$(SOC)/asm-offsets.s:	$(obj)include/autoconf.mk.dep
+$(obj)$(CPUDIR)/$(SOC)/asm-offsets.s:	$(obj)include/autoconf.mk.dep \
+	$(obj)include/spl-autoconf.mk
 	@mkdir -p $(obj)$(CPUDIR)/$(SOC)
 	if [ -f $(src)$(CPUDIR)/$(SOC)/asm-offsets.c ];then \
 		$(CC) -DDO_DEPS_ONLY \
@@ -711,7 +725,8 @@ include/license.h: tools/bin2header COPYING
 unconfig:
 	@rm -f $(obj)include/config.h $(obj)include/config.mk \
 		$(obj)board/*/config.tmp $(obj)board/*/*/config.tmp \
-		$(obj)include/autoconf.mk $(obj)include/autoconf.mk.dep
+		$(obj)include/autoconf.mk $(obj)include/autoconf.mk.dep \
+		$(obj)include/spl-autoconf.mk
 
 %_config::	unconfig
 	@$(MKCONFIG) -A $(@:_config=)
diff --git a/config.mk b/config.mk
index 51b4783..3246c2c 100644
--- a/config.mk
+++ b/config.mk
@@ -153,7 +153,13 @@ DTC	= dtc
 #########################################################################
 
 # Load generated board configuration
+ifeq ($(CONFIG_SPL_BUILD),y)
+# Include SPL autoconf
+sinclude $(OBJTREE)/include/spl-autoconf.mk
+else
+# Include normal autoconf
 sinclude $(OBJTREE)/include/autoconf.mk
+endif
 sinclude $(OBJTREE)/include/config.mk
 
 # Some architecture config.mk files need to know what CPUDIR is set to,
-- 
1.7.4.1