Commit 51148790 added scripts/multiconfig.py written in Python 2
to adjust Kconfig for U-Boot.

It has been hard for Python 3 users because Python 2 and Python 3
are not compatible with each other.

We are not happy about adding a new host tool dependency
(in this case, Python version dependency) for the core build process.
After some discussion, we decided to use only basic tools.

The script may get a bit more unreadable by shell scripting,
but we believe it is worthwhile.

In addition, this commit revives "<board>_config" target that is
equivalent to "<board>_defconfig" for backwards compatibility.
It is annoying to adjust various projects which use U-Boot.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Suggested-by: Igor Grinberg <grinberg@compulab.co.il>
Tested-by: Igor Grinberg <grinberg@compulab.co.il>
Acked-by: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@ti.com>
Cc: Jeroen Hofstee <jeroen@myspectrum.nl>
Cc: Stephen Warren <swarren@nvidia.com>

In Python, sys.exit() function can also take an object other
than an integer.

If an integer is given to the argument, Python exits with the return
code of it.  If a non-integer argument is given, Python outputs it
to stderr and exits with the return code of 1.

That means,

    print >> sys.stderr, "Blah Blah"
    sys.exit(1)

is equivalent to

    sys.exit("Blah Blah")

The latter is a useful shorthand.

Note:
Some error messages in Buildman and Patman were output to stdout.
But they should go to stderr.  They are also fixed by this commit.
This is a nice side effect.

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>