[PATCH v2 2/2] doc: add Arm Juno board documentation

[Andre Przywara]

The Juno Arm development board is an open, vendor-neutral, Armv8-A
development platform.
Add documentation that briefly outlines the hardware, and describes
building and installation of U-Boot.

Signed-off-by: Andre Przywara <andre.przywara at arm.com>
---
 doc/board/armltd/index.rst |   1 +
 doc/board/armltd/juno.rst  | 114 +++++++++++++++++++++++++++++++++++++
 2 files changed, 115 insertions(+)
 create mode 100644 doc/board/armltd/juno.rst

diff --git a/doc/board/armltd/index.rst b/doc/board/armltd/index.rst
index caa6fd2bb0..68d938c647 100644
--- a/doc/board/armltd/index.rst
+++ b/doc/board/armltd/index.rst
@@ -8,3 +8,4 @@ ARM Ltd. boards and emulated systems
    :maxdepth: 2
 
    fvp64
+   juno
diff --git a/doc/board/armltd/juno.rst b/doc/board/armltd/juno.rst
new file mode 100644
index 0000000000..3d20ff129c
--- /dev/null
+++ b/doc/board/armltd/juno.rst
@@ -0,0 +1,114 @@
+.. SPDX-License-Identifier: GPL-2.0
+.. Copyright (C) 2021 Arm Ltd.
+
+Arm Juno development platform
+=============================
+
+The `Juno development board`_ is an open, vendor-neutral, Armv8-A development
+platform, made by Arm Ltd. It is part of the Versatile Express family.
+There are three revisions of the board:
+
+* Juno r0, with two Cortex-A57 and four Cortex-A53 cores, without PCIe.
+* Juno r1, with two Cortex-A57 and four Cortex-A53 cores, in later silicon
+  revisions, and with PCIe slots, Gigabit Ethernet and two SATA ports.
+* Juno r2, with two Cortex-A72 and four Cortex-A53 cores, otherwise the
+  same as r1.
+
+Among other things, the motherboard contains a management controller (MCC),
+an FPGA providing I/O interfaces (IOFPGA) and 64MB of NOR flash. The provided
+platform devices resemble the VExpress peripherals.
+The actual SoC also contains a Cortex-M3 based System Control Processor (SCP).
+The `V2M-Juno TRM`_ contains more technical details.
+
+U-Boot build
+------------
+There is only one defconfig and one binary build that covers all three board
+revisions, so to generate the needed ``u-boot.bin``:
+
+.. code-block:: bash
+
+    $ make vexpress_aemv8a_juno_defconfig
+    $ make
+
+The automatic distro boot sequence looks for UEFI boot applications and
+``boot.scr`` scripts on various boot media, starting with USB, then on disks
+connected to the two SATA ports, PXE, DHCP and eventually on the NOR flash.
+
+U-Boot installation
+-------------------
+This assumes there is some firmware on the SD card or NOR flash (see below
+for more details). The U-Boot binary is included in the Trusted Firmware
+FIP image, so after building U-Boot, this needs to be repackaged or recompiled.
+
+The NOR flash will be updated by the MCC, based on the content of a micro-SD
+card, which is exported as a USB mass storage device via the rear USB-B
+socket. So to access that SD card, connect a cable to some host computer, and
+mount the FAT16 partition of the UMS device.
+If there is no device, check the upper serial port for a prompt, and
+explicitly enable the USB interface::
+
+    Cmd> usb_on
+    Enabling debug USB...
+
+Repackaging an existing FIP image
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+To prevent problems, it is probably a good idea to backup the existing firmware,
+for instance by just copying the entire ``SOFTWARE/`` directory, or at least
+the current ``fip.bin``, beforehand.
+
+To just replace the BL33 image in the exising FIP image, you can use
+`fiptool`_ from the Trusted Firmware repository, on the image file:
+
+.. code-block:: bash
+
+    $ git clone https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git
+    $ cd trusted-firmware-a
+    $ make fiptool
+    $ tools/fiptool/fiptool update --nt-fw=/path/to/your/u-boot.bin /mnt/juno/SOFTWARE/fip.bin
+
+Unmount the USB mass storage device and reboot the board, the new ``fip.bin``
+will be automatically written to the NOR flash and then used.
+
+Rebuilding Trusted Firmware
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+You can also generate a new FIP image by compiling Arm Trusted Firmware,
+and providing ``u-boot.bin`` as the BL33 file. For that you can either build
+the required `SCP firmware`_ yourself, or just extract the existing
+version from your ``fip.bin``, using `fiptool`_ (see above):
+
+.. code-block:: bash
+
+    $ mkdir /tmp/juno; cd /tmp/juno
+    $ fiptool unpack /mnt/juno/SOFTWARE/fip.bin
+
+Then build TF-A:
+
+.. code-block:: bash
+
+    $ git clone https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git
+    $ cd trusted-firmware-a
+    $ make CROSS_COMPILE=aarch64-linux-gnu- PLAT=juno DEBUG=1 \
+      SCP_BL2=/tmp/juno/scp-fw.bin BL33=/path/to/your/u-boot.bin fiptool all fip
+    $ cp build/juno/debug/bl1.bin build/juno/debug/fip.bin /mnt/juno/SOFTWARE
+
+Then umount the USB device, and reboot, as above.
+
+Device trees
+------------
+The device tree files for the boards are maintained in the Linux kernel
+repository. They end up in the ``SOFTWARE/`` directory of the SD card, as
+``juno.dtb``, ``juno-r1.dtb``, and ``juno-r2.dtb``, respectively. The MCC
+firmware will look into the images.txt file matching the board revision, from
+the ``SITE1/`` directory. Each version there will reference its respective DTB
+file in ``SOFTWARE/``, and so the correct version will end in the NOR flash, in
+the ``board.dtb`` partition. U-Boot picks its control DTB from there, you can
+pass this on to a kernel using ``$fdtcontroladdr``.
+
+You can update the DTBs anytime, by building them using the ``dtbs`` make
+target from a Linux kernel tree, then just copying the generated binaries
+to the ``SOFTWARE/`` directory of the SD card.
+
+.. _`Juno development board`: https://developer.arm.com/tools-and-software/development-boards/juno-development-board
+.. _`V2M-Juno TRM`: https://developer.arm.com/documentation/100113/latest
+.. _`fiptool`: https://github.com/ARM-software/arm-trusted-firmware/tree/master/tools/fiptool
+.. _`SCP firmware`: https://github.com/ARM-software/SCP-firmware.git
-- 
2.25.1