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+.. SPDX-License-Identifier: GPL-2.0+
+.. Copyright 2014 Broadcom Corporation.
+
+Semihosting
+===========
+
+Semihosting is ARM's way of having a real or virtual target communicate
+with a host or host debugger for basic operations such as file I/O,
+console I/O, etc. Please see `Arm's semihosting documentation
+<https://developer.arm.com/documentation/100863/latest/>`_ for more
+information.
+
+Platform Support
+----------------
+
+Versatile Express
+^^^^^^^^^^^^^^^^^
+
+For developing on armv8 virtual fastmodel platforms, semihosting is a
+valuable tool since it allows access to image/configuration files before
+eMMC or other NV media are available.
+
+There are two main ARM virtual Fixed Virtual Platform (FVP) models,
+`Versatile Express (VE) FVP and BASE FVP
+<http://www.arm.com/products/tools/models/fast-models/foundation-model.php>`_.
+The initial vexpress64 u-boot board created here runs on the VE virtual
+platform using the license-free Foundation_v8 simulator. Fortunately,
+the Foundation_v8 simulator also supports the BASE_FVP model which
+companies can purchase licenses for and contain much more functionality.
+So we can, in U-Boot, run either model by either using the VE FVP (default),
+or turning on ``CONFIG_BASE_FVP`` for the more full featured model.
+
+Rather than create a new armv8 board similar to ``armltd/vexpress64``, add
+semihosting calls to the existing one, enabled with ``CONFIG_SEMIHOSTING``
+and ``CONFIG_BASE_FVP`` both set. Also reuse the existing board config file
+vexpress_aemv8.h but differentiate the two models by the presence or
+absence of ``CONFIG_BASE_FVP``. This change is tested and works on both the
+Foundation and Base fastmodel simulators.
+
+QEMU
+^^^^
+
+Another ARM emulator which supports semihosting is `QEMU
+<https://www.qemu.org/>`_. To enable semihosting, enable
+``CONFIG_SERIAL_PROBE_ALL`` when configuring U-Boot, and use
+``-semihosting`` when invoking QEMU. Adding ``-nographic`` can also be
+helpful. When using a semihosted serial console, QEMU will block waiting
+for input. This will cause the GUI to become unresponsive. To mitigate
+this, try adding ``-nographic``. For more information about building and
+running QEMU, refer to the :doc:`board documentation
+<../board/emulation/qemu-arm>`.
+
+OpenOCD
+^^^^^^^
+
+Any ARM platform can use semihosting with an attached debugger. One such
+debugger with good support for a variety of boards and JTAG adapters is
+`OpenOCD <https://openocd.org/>`_. Semihosting is not enabled by default,
+so you will need to enable it::
+
+    $ openocd -f <your board config> -c init -c halt -c \
+          'arm semihosting enable' -c resume
+
+Note that enabling semihosting can only be done after attaching to the
+board with ``init``, and must be done while the CPU is halted. For a more
+extended example, refer to the :ref:`LS1046ARDB docs <ls1046ardb_jtag>`.
+
+Loading files
+-------------
+
+The semihosting code adds a "semihosting filesystem"::
+
+  load hostfs - <address> <image>
+
+That will load an image from the host filesystem into RAM at the specified
+address. If you are using U-Boot SPL, you can also use ``BOOT_DEVICE_SMH``
+which will load ``CONFIG_SPL_FS_LOAD_PAYLOAD_NAME``.
+
+Host console
+------------
+
+U-Boot can use the host's console instead of a physical serial device by
+enabling ``CONFIG_SERIAL_SEMIHOSTING``. If you don't have
+``CONFIG_DM_SERIAL`` enabled, make sure you disable any other serial
+drivers.
+
+Migrating from ``smhload``
+--------------------------
+
+If you were using the ``smhload`` command, you can migrate commands like::
+
+    smhload <file> <address> [<end var>]
+
+to a generic load command like::
+
+    load hostfs - <address> <file>
+
+The ``load`` command will set the ``filesize`` variable with the size of
+the file. The ``fdt chosen`` command has been updated to take a size
+instead of an end address. If you were adding the initramfs to your device
+tree like::
+
+    fdt chosen <address> <end var>
+
+you can now run::
+
+    fdt chosen <address> $filesize