When Kconfig for U-boot was examined, one of the biggest issues was
how to support multiple images (Normal, SPL, TPL).  There were
actually two options, "single .config" and "multiple .config".
After some discussions and thought experiments, I chose the latter,
i.e. to create ".config", "spl/.config", "tpl/.config" for Normal,
SPL, TPL, respectively.

It is true that the "multiple .config" strategy provided us the
maximum flexibility and helped to avoid duplicating CONFIGs among
Normal, SPL, TPL, but I have noticed some fatal problems:

[1] It is impossible to share CONFIG options across the images.
  If you change the configuration of Main image, you often have to
  adjust some SPL configurations correspondingly.  Currently, we
  cannot handle the dependencies between them.  It means one of the
  biggest advantages of Kconfig is lost.

[2] It is too painful to change both ".config" and "spl/.config".
  Sunxi guys started to work around this problem by creating a new
  configuration target.  Commit cbdd9a97 (sunxi: kconfig: Add
  %_felconfig rule to enable FEL build of sunxi platforms.) added
  "make *_felconfig" to enable CONFIG_SPL_FEL on both images.
  Changing the configuration of multiple images in one command is a
  generic demand.  The current implementation cannot propose any
  good solution about this.

[3] Kconfig files are getting ugly and difficult to understand.
  Commit b724bd7d (dm: Kconfig: Move CONFIG_SYS_MALLOC_F_LEN to
  Kconfig) has sprinkled "if !SPL_BUILD" over the Kconfig files.

[4] The build system got more complicated than it should be.
  To adjust Linux-originated Kconfig to U-Boot, the helper script
  "scripts/multiconfig.sh" was introduced.  Writing a complicated
  text processor is a shell script sometimes caused problems.

Now I believe the "single .config" will serve us better.  With it,
all the problems above would go away.  Instead, we will have to add
some CONFIG_SPL_* (and CONFIG_TPL_*) options such as CONFIG_SPL_DM,
but we will not have much.  Anyway, this is what we do now in
scripts/Makefile.spl.

I admit my mistake with my apology and this commit switches to the
single .config configuration.

It is not so difficult to do that:

 - Remove unnecessary processings from scripts/multiconfig.sh
  This file will remain for a while to support the current defconfig
  format.  It will be removed after more cleanups are done.

 - Adjust some makefiles and Kconfigs

 - Add some entries to include/config_uncmd_spl.h and the new file
   scripts/Makefile.uncmd_spl.  Some CONFIG options that are not
   supported on SPL must be disabled because one .config is shared
   between SPL and U-Boot proper going forward.  I know this is not
   a beautiful solution and I think we can do better, but let's see
   how much we will have to describe them.

 - update doc/README.kconfig

More cleaning up patches will follow this.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

In U-Boot, SoC-specific headers are placed in
arch/$(ARCH)/include/asm/arch-$(SOC) and a symbolic link to that
directory is created at the early stage of the build process.

Creating and removing a symbolic link during the build is not
preferred.  In fact, Linux Kernel did away with include/asm-$(ARCH)
directories a long time time ago.

As for ARM, now it is possible to collect SoC sources into
arch/arm/mach-$(SOC).  It is also reasonable to move SoC headers
into arch/arm/mach-$(SOC)/include/mach.

This commit prepares for that.
If the directory arch/$(ARCH)/mach-$(SOC)/include/mach exists,
a symbolic to that directory is created.  Otherwise, a symbolic link
to arch/$(ARCH)/include/asm/arch-$(SOC) or arch-$(CPU) is created.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>

Since Linux 3.15, relative path feature and related fixes,
cleanups have been merged to the top Makefile.

The relative path feature looks stable enough, so let's import it
to U-Boot along with various cleanups.

Commits imported from Linux (some need adjustment) are:

[1] commit 7e1c04779efd by Michal Marek
  kbuild: Use relative path for $(objtree)

[2] commit 890676c65d69 by Michal Marek
  kbuild: Use relative path when building in the source tree

[3] commit 9da0763bdd82 by Michal Marek
  kbuild: Use relative path when building in a subdir of the source tree

[4] commit c2e28dc975ea by Michal Marek
  kbuild: Print the name of the build directory

[5] commit 066b7ed95580 by Michal Marek
  kbuild: Do not print the build directory with make -s

[6] commit 3f1d9a6cec01 by Michal Marek
  kbuild: make -s should be used with kernelrelease/kernelversion/image_name

[7] commit 7ff525712acf by Masahiro Yamada
  kbuild: fake the "Entering directory ..." message more simply

[8] commit 745a254322c8 by Masahiro Yamada
  kbuild: use $(Q) for sub-make target

[9] commit aa55c8e2f7a3 by Masahiro Yamada
  kbuild: handle C=... and M=... after entering into build directory

[10] commit ab7474ea5361 by Borislav Petkov
  Kbuild: Ignore GREP_OPTIONS env variable

To use relative path feature, tools/Makefile and scripts/Makefile.autoconf
must be tweaked.

Signed-off-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>

Now config_cmd_defaults.h is empty so it can be deleted safely.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>

This commit enables Kconfig.
Going forward, we use Kconfig for the board configuration.
mkconfig will never be used. Nor will include/config.mk be generated.

Kconfig must be adjusted for U-Boot because our situation is
a little more complicated than Linux Kernel.
We have to generate multiple boot images (Normal, SPL, TPL)
from one source tree.
Each image needs its own configuration input.

Usage:

Run "make <board>_defconfig" to do the board configuration.

It will create the .config file and additionally spl/.config, tpl/.config
if SPL, TPL is enabled, respectively.

You can use "make config", "make menuconfig" etc. to create
a new .config or modify the existing one.

Use "make spl/config", "make spl/menuconfig" etc. for spl/.config
and do likewise for tpl/.config file.

The generic syntax of configuration targets for SPL, TPL is:

  <target_image>/<config_command>

Here, <target_image> is either 'spl' or 'tpl'
      <config_command> is 'config', 'menuconfig', 'xconfig', etc.

When the configuration is done, run "make".
(Or "make <board>_defconfig all" will do the configuration and build
in one time.)

For futher information of how Kconfig works in U-Boot,
please read the comment block of scripts/multiconfig.py.

By the way, there is another item worth remarking here:
coexistence of Kconfig and board herder files.

Prior to Kconfig, we used C headers to define a set of configs.

We expect a very long term to migrate from C headers to Kconfig.
Two different infractructure must coexist in the interim.

In our former configuration scheme, include/autoconf.mk was generated
for use in makefiles.
It is still generated under include/, spl/include/, tpl/include/ directory
for the Normal, SPL, TPL image, respectively.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>