buildman: Add the option to download toolchains from kernel.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 VaĊĦut <marex@denx.de>
Suggested-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/README b/tools/buildman/README
index 849e6ca..cf7bf5c 100644
--- a/tools/buildman/README
+++ b/tools/buildman/README
@@ -173,9 +173,9 @@
 
 3. Make sure you have the require Python pre-requisites
 
-Buildman uses multiprocessing, Queue, shutil, StringIO and ConfigParser.
-These should normally be available, but if you get an error like this then
-you will need to obtain those modules:
+Buildman uses multiprocessing, Queue, shutil, StringIO, ConfigParser and
+urllib2. These should normally be available, but if you get an error like
+this then you will need to obtain those modules:
 
     ImportError: No module named multiprocessing
 
@@ -310,6 +310,47 @@
 be used (c88 and c99). This is a feature.
 
 
+5. Install new toolchains if needed
+
+You can download toolchains and update the [toolchain] section of the
+settings file to find them.
+
+To make this easier, buildman can automatically download and install
+toolchains from kernel.org. First list the available architectures:
+
+$ ./tools/buildman/buildman sandbox --fetch-arch list
+Checking: https://www.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.6.3/
+Checking: https://www.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.6.2/
+Checking: https://www.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.5.1/
+Checking: https://www.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.2.4/
+Available architectures: alpha am33_2.0 arm avr32 bfin cris crisv32 frv h8300
+hppa hppa64 i386 ia64 m32r m68k mips mips64 or32 powerpc powerpc64 s390x sh4
+sparc sparc64 tilegx x86_64 xtensa
+
+Then pick one and download it:
+
+$ ./tools/buildman/buildman sandbox --fetch-arch or32
+Checking: https://www.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.6.3/
+Checking: https://www.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.6.2/
+Checking: https://www.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.5.1/
+Downloading: https://www.kernel.org/pub/tools/crosstool/files/bin/x86_64/4.5.1//x86_64-gcc-4.5.1-nolibc_or32-linux.tar.xz
+Unpacking to: /home/sjg/.buildman-toolchains
+Testing
+      - looking in '/home/sjg/.buildman-toolchains/gcc-4.5.1-nolibc/or32-linux/.'
+      - looking in '/home/sjg/.buildman-toolchains/gcc-4.5.1-nolibc/or32-linux/bin'
+         - found '/home/sjg/.buildman-toolchains/gcc-4.5.1-nolibc/or32-linux/bin/or32-linux-gcc'
+Tool chain test:  OK
+
+Buildman should now be set up to use your new toolchain.
+
+At the time of writing, U-Boot has these architectures:
+
+   arc, arm, avr32, blackfin, m68k, microblaze, mips, nds32, nios2, openrisc
+   powerpc, sandbox, sh, sparc, x86
+
+Of these, only arc, microblaze and nds32 are not available at kernel.org..
+
+
 How to run it
 =============