Makefile: prepare for using Kbuild-style Makefile

Every makefile in sub directories has common lines
at the top and the bottom.
This commit pushes the common parts into script/Makefile.build.

Going forward sub-makefiles only need to describe this part:

    COBJS := ...
    COBJS += ...
    SOBJS := ...

But using obj-y is preferable to prepare for switching to Kbuild.

The conventional (non-Kbuild) Makefile style is still supported.
This is achieved by greping the Makefile before entering into it.
U-Boot conventional sub makefiles always include some other makefiles.
So the build system searches a line beginning with "include" keyword
in the makefile in order to distinguish which style it is.
If the Makefile include a "include" line, we assume it is a conventional
U-Boot style. Otherwise, it is treated as a Kbuild-style makefile.

With this tweak, we can switch sub-makefiles
from U-Boot style to Kbuild style little by little.

obj-y := foo/
syntax (descending into the sub directory) is not supportd yet.
It will be implemented in the upcomming commit.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@ti.com>

Makefile

@@ -595,14 +595,32 @@ ifeq ($(CONFIG_KALLSYMS),y)
 		$(GEN_UBOOT) $(obj)common/system_map.o
 endif
 
+# Tentative step for Kbuild-style makefiles coexist with conventional U-Boot style makefiles
+#  U-Boot conventional sub makefiles always include some other makefiles.
+#  So, the build system searches a line beginning with "include" before entering into the sub makefile
+#  in order to distinguish which style it is.
+#  If the Makefile include a "include" line, we assume it is an U-Boot style makefile.
+#  Otherwise, it is treated as a Kbuild-style makefile.
+select_makefile = \
+	+if grep -q "^include" $1/Makefile; then				\
+		$(MAKE) -C $1;						\
+	else								\
+		$(MAKE) -C $1 -f $(TOPDIR)/scripts/Makefile.build;	\
+		mv $(dir $@)built-in.o $@;				\
+	fi
+
+# We do not need to build $(OBJS) explicitly.
+# It is built while we are at $(CPUDIR)/lib$(CPU).o build.
 $(OBJS):	depend
-		$(MAKE) -C $(CPUDIR) $(if $(REMOTE_BUILD),$@,$(notdir $@))
+		if grep -q "^include" $(CPUDIR)/Makefile; then \
+			$(MAKE) -C $(CPUDIR) $(if $(REMOTE_BUILD),$@,$(notdir $@)); \
+		fi
 
 $(LIBS):	depend $(SUBDIR_TOOLS)
-		$(MAKE) -C $(dir $(subst $(obj),,$@))
+		+$(call select_makefile, $(dir $(subst $(obj),,$@)))
 
 $(LIBBOARD):	depend $(LIBS)
-		$(MAKE) -C $(dir $(subst $(obj),,$@))
+		+$(call select_makefile, $(dir $(subst $(obj),,$@)))
 
 $(SUBDIRS):	depend
 		$(MAKE) -C $@ all
@@ -630,6 +648,13 @@ $(obj)tpl/u-boot-tpl.bin:	$(SUBDIR_TOOLS) depend
 updater:
 		$(MAKE) -C tools/updater all
 
+select_makefile2 = \
+	if grep -q "^include" $1/Makefile; then					\
+		$(MAKE) -C $1 _depend;						\
+	else									\
+		$(MAKE) -C $1 -f $(TOPDIR)/scripts/Makefile.build _depend;	\
+	fi
+
 # Explicitly make _depend in subdirs containing multiple targets to prevent
 # parallel sub-makes creating .depend files simultaneously.
 depend dep:	$(TIMESTAMP_FILE) $(VERSION_FILE) \
@@ -638,8 +663,9 @@ depend dep:	$(TIMESTAMP_FILE) $(VERSION_FILE) \
 		$(obj)include/autoconf.mk \
 		$(obj)include/generated/generic-asm-offsets.h \
 		$(obj)include/generated/asm-offsets.h
-		for dir in $(SUBDIRS) $(CPUDIR) $(LDSCRIPT_MAKEFILE_DIR) ; do \
-			$(MAKE) -C $$dir _depend ; done
+		+for dir in $(SUBDIRS) $(CPUDIR) $(LDSCRIPT_MAKEFILE_DIR) ; do \
+			$(call select_makefile2, $$dir); \
+		done
 
 TAG_SUBDIRS = $(SUBDIRS)
 TAG_SUBDIRS += $(dir $(__LIBS))

scripts/Makefile.build

@@ -0,0 +1,48 @@
+# our default target
+.PHONY: all
+all:
+
+include $(TOPDIR)/config.mk
+
+LIB := $(obj)built-in.o
+LIBGCC = $(obj)libgcc.o
+SRCS :=
+
+include Makefile
+
+# Backward compatible: obj-y is preferable
+COBJS := $(sort $(COBJS) $(COBJS-y))
+SOBJS := $(sort $(SOBJS) $(SOBJS-y))
+
+# Going forward use the following
+obj-y := $(sort $(obj-y))
+extra-y := $(sort $(extra-y))
+lib-y := $(sort $(lib-y))
+
+SRCS	+= $(COBJS:.o=.c) $(SOBJS:.o=.S) \
+ $(wildcard $(obj-y:.o=.c) $(obj-y:.o=.S) $(lib-y:.o=.c) $(lib-y:.o=.S) $(extra-y:.o=.c) $(extra-y:.o=.S))
+OBJS	:= $(addprefix $(obj),$(COBJS) $(SOBJS) $(obj-y))
+
+LGOBJS := $(addprefix $(obj),$(sort $(GLSOBJS) $(GLCOBJS)) $(lib-y))
+
+all: $(LIB) $(addprefix $(obj),$(extra-y))
+
+$(LIB):	$(obj).depend $(OBJS)
+	$(call cmd_link_o_target, $(OBJS))
+
+ifneq ($(strip $(lib-y)),)
+all: $(LIBGCC)
+
+$(LIBGCC): $(obj).depend $(LGOBJS)
+	$(call cmd_link_o_target, $(LGOBJS))
+endif
+
+#########################################################################
+
+# defines $(obj).depend target
+
+include $(TOPDIR)/rules.mk
+
+sinclude $(obj).depend
+
+#########################################################################

spl/Makefile

@@ -200,11 +200,29 @@ GEN_UBOOT = \
 $(obj)$(SPL_BIN):	depend $(START) $(LIBS) $(obj)u-boot-spl.lds
 	$(GEN_UBOOT)
 
+# Tentative step for Kbuild-style makefiles coexist with conventional U-Boot style makefiles
+#  U-Boot conventional sub makefiles always include some other makefiles.
+#  So, the build system searches a line beginning with "include" before entering into the sub makefile
+#  in order to distinguish which style it is.
+#  If the Makefile include a "include" line, we assume it is an U-Boot style makefile.
+#  Otherwise, it is treated as a Kbuild-style makefile.
+select_makefile = \
+	if grep -q "^include" $1/Makefile; then				\
+		$(MAKE) -C $1;						\
+	else								\
+		$(MAKE) -C $1 -f $(TOPDIR)/scripts/Makefile.build;	\
+		mv $(dir $@)built-in.o $@;				\
+	fi
+
+# We do not need to build $(START) explicitly.
+# It is built while we are at $(CPUDIR)/lib$(CPU).o build.
 $(START):	depend
-	$(MAKE) -C $(SRCTREE)/$(START_PATH) $@
+	if grep -q "^include" $(SRCTREE)$(dir $(subst $(SPLTREE),,$@))Makefile; then \
+		$(MAKE) -C $(SRCTREE)/$(START_PATH) $@; \
+	fi
 
 $(LIBS):	depend
-	$(MAKE) -C $(SRCTREE)$(dir $(subst $(SPLTREE),,$@))
+	+$(call select_makefile, $(SRCTREE)$(dir $(subst $(SPLTREE),,$@)))
 
 $(obj)u-boot-spl.lds: $(LDSCRIPT) depend
 	$(CPP) $(CPPFLAGS) $(LDPPFLAGS) -I$(obj). -ansi -D__ASSEMBLY__ -P - < $< > $@