One use-case for buildman is to continually run it interactively after
each small step in a large refactoring operation. This gives more
immediate feedback than making a number of commits and then going back and
testing them. For this to work well, buildman needs to be extremely fast.
At present, a couple issues prevent it being as fast as it could be:

1) Each time buildman runs "make %_defconfig", it runs "make mrproper"
first. This throws away all previous build results, requiring a
from-scratch build. Optionally avoiding this would speed up the build, at
the cost of potentially causing or missing some build issues.

2) A build tree is created per thread rather than per board. When a thread
switches between building different boards, this often causes many files
to be rebuilt due to changing config options. Using a separate build tree
for each board would avoid this. This does put more strain on the system's
disk cache, but it is worth it on my system at least.

This commit adds two command-line options to implement the changes
described above; -I ("--incremental") turns of "make mrproper" and -P
("--per-board-out-dir") creats a build directory per board rather than per
thread.

Tested:

    ./tools/buildman/buildman.py tegra
    ./tools/buildman/buildman.py -I -P tegra
    ./tools/buildman/buildman.py -b tegra_dev tegra
    ./tools/buildman/buildman.py -b tegra_dev -I -P tegra

... each once after deleting the buildman result/work directory, and once
"incrementally" after a previous identical invocation.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Acked-by: Simon Glass <sjg@chromium.org> # v1
Tested-by: Simon Glass <sjg@chromium.org> # v1
Acked-by: Simon Glass <sjg@chromium.org>

It is convenient to install symlinks to buildman and patman in the search
patch, such as /usr/local/bin. But when this is done, the -H option fails to
work because it looks in the directory containing the symlink instead of its
target. Fix this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>

It is useful to be able to see CONFIG changes made by commits. Add this
feature to buildman using the -K flag so that all CONFIG changes are
reported.

The CONFIG options exist in a number of files. Each is reported
individually as well as a summary that covers all files. The output
shows three parts: green for additions, red for removals and yellow for
changes.

Signed-off-by: Simon Glass <sjg@chromium.org>

Normally buildman runs with 'make -s' meaning that only errors and warnings
appear in the log file. Add a -V option to run make in verbose mode, and
with V=1, causing a full build log to be created.

Signed-off-by: Simon Glass <sjg@chromium.org>

The site at https://www.kernel.org/pub/tools/crosstool/ is a convenient
repository of toolchains which can be used for U-Boot. Add a feature to
download and install a toolchain for a selected architecture automatically.

It isn't clear how long this site will stay in the current place and
format, but we should be able to rely on bug reports if it changes.

Suggested-by: Marek Vašut <marex@denx.de>
Suggested-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Simon Glass <sjg@chromium.org>

In some cases there may be multiple toolchains with the same name in the
path. Provide an option to use the full path in the CROSS_COMPILE
environment variable.

Note: Wolfgang mentioned that this is dangerous since in some cases there
may be other tools on the path that are needed. So this is set up as an
option, not the default. I will need test confirmation (i.e. that this
commit fixes a real problem) before merging it.

Signed-off-by: Simon Glass <sjg@chromium.org>
Suggested-by: Steve Rae <srae@broadcom.com>

Adjust the -b flag to permit a range expression as well as a branch.

Signed-off-by: Simon Glass <sjg@chromium.org>
Suggested-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Tested-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>

When running tests the output directory is often wiped. This is only safe if
a branch is being built. The output directory may contain other things
besides the buildman test output.

Signed-off-by: Simon Glass <sjg@chromium.org>

When building current source for a single board, buildman puts the output
in <output_dir>/current/current/<board>. Add an option to make it use
<output_dir>/<board> instead. This removes the unnecessary directories
in that case, controlled by the --no-subdirs/-N option.

Suggested-by: Tom Rini <trini@ti.com>
Signed-off-by: Simon Glass <sjg@chromium.org>

Buildman normally obtains the upstream commit by asking git. Provided that
the branch was created with 'git checkout -b <branch> <some_upstream>' then
this normally works.

When there is no upstream, we can try to guess one, by looking up through
the commits until we find a branch. Add a function to try this and print
a warning if buildman ends up relying on it.

Also update the documentation to match.

Signed-off-by: Simon Glass <sjg@chromium.org>
Suggested-by: Wolfgang Denk <wd@denx.de>