scripts: allow building USB loader tools for target as well

We currently build the USB loader tools only for the host (build) system,
but it can be useful to cross compile them as well for the target.

We already have some target tools, but support for those is easier,
because they don't link against libraries. We use pkg-config to get
cc and ld flags, but we always assume that pkg-config is for the host
system and there is no well-defined way to request pkg-config for the
target system.

Support this by introducing a new CROSS_PKG_CONFIG. This will be
consulted only for target tools and default to
$(CROSS_COMPILE)pkgconfig.

Users can override it as necessary, for example, with Yocto, pkg-config
will be for the cross environment, so target tools can now be built
with:

  export ARCH=sandbox CROSS_COMPILE=aarch64-linux-gnu-
  export CROSS_PKG_CONFIG=pkg-config scripts
  make targettools_defconfig
  make scripts

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20210917174127.23345-4-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 45 insertions, 0 deletions

diff --git a/Documentation/user/barebox.rst b/Documentation/user/barebox.rst
index 503f0b9797..b6b7a57af3 100644
--- a/Documentation/user/barebox.rst
+++ b/Documentation/user/barebox.rst
@@ -262,3 +262,48 @@ the usage for a particular command. barebox has tab completion which will comple
 your command. Arguments to commands are also completed depending on the command. If
 a command expects a file argument only files will be offered as completion. Other
 commands will only complete devices or devicetree nodes.
+
+Building barebox tools
+----------------------
+
+The normal barebox build results in one or more barebox images (cf. :ref:`multi_image`)
+and a number of tools built from its ``scripts/`` directory.
+
+Most tools are used for the barebox build itself: e.g. the device tree compiler,
+the Kconfig machinery and the different image formatting tools that wrap barebox,
+so it may be loaded by the boot ROM of the relevant SoCs.
+
+In addition to these barebox also builds host and target tools that are useful
+outside of barebox build: e.g. to manipulate the environment or to load an
+image over a boot ROM's USB recovery protocol.
+
+There are two ``ARCH=sandbox`` to make this more straight forward:
+
+Host Tools
+^^^^^^^^^^
+
+The ``hosttools_defconfig`` will compile standalone host tools for the
+host (build) system. To build the USB loaders, ``pkg-config`` needs to know
+about ``libusb-1.0``.
+
+.. code-block:: console
+
+  export ARCH=sandbox
+  make hosttools_defconfig
+  make scripts
+
+Target Tools
+^^^^^^^^^^^^
+
+The ``targettools_defconfig`` will cross-compile standalone target tools for the
+target system.  To build the USB loaders, ``CROSS_PKG_CONFIG`` needs to know
+about ``libusb-1.0``. This config won't built any host tools, so it's ok to
+set ``CROSS_PKG_CONFIG=pkg-config`` if ``pkg-config`` is primed for target
+use. The default is ``CROSS_PKG_CONFIG=$(CROSS_COMPILE)pkg-config``. Example:
+
+.. code-block:: console
+
+  export ARCH=sandbox CROSS_COMPILE=aarch64-linux-gnu-
+  export CROSS_PKG_CONFIG=pkg-config
+  make targettools_defconfig
+  make scripts