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, 2 insertions, 2 deletions

diff --git a/board/matrix_vision/mvblm7/Makefile b/board/matrix_vision/mvblm7/Makefile
index 879d7946554..1bc1d61dcf6 100644
--- a/board/matrix_vision/mvblm7/Makefile
+++ b/board/matrix_vision/mvblm7/Makefile
@@ -8,5 +8,5 @@ obj-y	:= mvblm7.o pci.o fpga.o
 
 extra-y := bootscript.img
 
-$(obj)bootscript.img:
-	@mkimage -T script -C none -n M7_script -d bootscript $@
+$(obj)/bootscript.img: $(src)/bootscript
+	@mkimage -T script -C none -n M7_script -d $< $@