kbuild: change out-of-tree build

This commit changes the working directory
where the build process occurs.

Before this commit, build process occurred under the source
tree for both in-tree and out-of-tree build.

That's why we needed to add $(obj) prefix to all generated
files in makefiles like follows:
  $(obj)u-boot.bin:  $(obj)u-boot

Here, $(obj) is empty for in-tree build, whereas it points
to the output directory for out-of-tree build.

And our old build system changes the current working directory
with "make -C <sub-dir>" syntax when descending into the
sub-directories.

On the other hand, Kbuild uses a different idea
to handle out-of-tree build and directory descending.

The build process of Kbuild always occurs under the output tree.
When "O=dir/to/store/output/files" is given, the build system
changes the current working directory to that directory and
restarts the make.

Kbuild uses "make -f $(srctree)/scripts/Makefile.build obj=<sub-dir>"
syntax for descending into sub-directories.
(We can write it like "make $(obj)=<sub-dir>" with a shorthand.)
This means the current working directory is always the top
of the output directory.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Tested-by: Gerhard Sittig <gsi@denx.de>

1 files changed, 11 insertions, 19 deletions

diff --git a/nand_spl/board/sheldon/simpc8313/Makefile b/nand_spl/board/sheldon/simpc8313/Makefile
index 5e83abc..ca45ecd 100644
--- a/nand_spl/board/sheldon/simpc8313/Makefile
+++ b/nand_spl/board/sheldon/simpc8313/Makefile
@@ -19,8 +19,8 @@ SOBJS	= start.o ticks.o
 COBJS	= nand_boot_fsl_elbc.o $(BOARD).o sdram.o ns16550.o spl_minimal.o \
 	  time.o cache.o
 
-SRCS	:= $(addprefix $(obj),$(SOBJS:.o=.S) $(COBJS:.o=.c))
-OBJS	:= $(addprefix $(obj),$(SOBJS) $(COBJS))
+SRCS	:= $(addprefix $(obj)/,$(SOBJS:.o=.S) $(COBJS:.o=.c))
+OBJS	:= $(addprefix $(obj)/,$(SOBJS) $(COBJS))
 __OBJS	:= $(SOBJS) $(COBJS)
 LNDIR	:= $(nandobj)board/$(BOARDDIR)
 
@@ -41,46 +41,38 @@ $(nandobj)u-boot.lds: $(LDSCRIPT)
 
 # create symbolic links for common files
 
-$(obj)start.S:
+$(obj)/start.S:
 	@rm -f $@
 	ln -s $(SRCTREE)/arch/powerpc/cpu/mpc83xx/start.S $@
 
-$(obj)nand_boot_fsl_elbc.c:
+$(obj)/nand_boot_fsl_elbc.c:
 	@rm -f $@
 	ln -s $(SRCTREE)/nand_spl/nand_boot_fsl_elbc.c $@
 
-$(obj)sdram.c:
+$(obj)/sdram.c:
 	@rm -f $@
 	ln -s $(SRCTREE)/board/$(BOARDDIR)/sdram.c $@
 
-$(obj)$(BOARD).c:
+$(obj)/$(BOARD).c:
 	@rm -f $@
 	ln -s $(SRCTREE)/board/$(BOARDDIR)/$(BOARD).c $@
 
-$(obj)ns16550.c:
+$(obj)/ns16550.c:
 	@rm -f $@
 	ln -s $(SRCTREE)/drivers/serial/ns16550.c $@
 
-$(obj)spl_minimal.c:
+$(obj)/spl_minimal.c:
 	@rm -f $@
 	ln -s $(SRCTREE)/arch/powerpc/cpu/mpc83xx/spl_minimal.c $@
 
-$(obj)cache.c:
+$(obj)/cache.c:
 	@rm -f $@
 	ln -s $(SRCTREE)/arch/powerpc/lib/cache.c $@
 
-$(obj)time.c:
+$(obj)/time.c:
 	@rm -f $@
 	ln -s $(SRCTREE)/arch/powerpc/lib/time.c $@
 
-$(obj)ticks.S:
+$(obj)/ticks.S:
 	@rm -f $@
 	ln -s $(SRCTREE)/arch/powerpc/lib/ticks.S $@
-
-#########################################################################
-
-$(obj)%.o:	$(obj)%.S
-	$(CC) $(AFLAGS) -c -o $@ $<
-
-$(obj)%.o:	$(obj)%.c
-	$(CC) $(CFLAGS) -c -o $@ $<