doc: boards: amlogic: update for Radxa Zero

Add documentation bits for the Radxa Zero

Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
[narmstrong: updated u200 MAINTAINERS]
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>

board/amlogic/u200/MAINTAINERS

@@ -7,3 +7,4 @@ F:	configs/u200_defconfig
 F:	configs/bananapi-m5_defconfig
 F:	configs/radxa-zero_defconfig
 F:	doc/board/amlogic/u200.rst
+F:	doc/board/amlogic/radxa-zero.rst

doc/board/amlogic/index.rst

@@ -17,7 +17,7 @@ This matrix concerns the actual source code version.
 +===============================+===========+=================+==============+=============+============+=============+==============+
 | Boards                        | Odroid-C2 | P212            | Khadas VIM2  | S400        | U200       | Odroid-N2   | SEI610       |
 |                               | Nanopi-K2 | Khadas-VIM      | Libretech-PC | JetHub J100 | SEI510     | Khadas-VIM3 | Khadas-VIM3L |
-|                               | P200      | LibreTech-CC v1 | WeTek Core2  |             |            | GT-King/Pro | Odroid-C4    |
+|                               | P200      | LibreTech-CC v1 | WeTek Core2  |             | Radxa Zero | GT-King/Pro | Odroid-C4    |
 |                               | P201      | LibreTech-AC v2 |              |             |            | GSKing-X    | Odroid-HC4   |
 |                               |           | JetHub J80      |              |             |            |             | BananaPi-M5  |
 +-------------------------------+-----------+-----------------+--------------+-------------+------------+-------------+--------------+
@@ -98,6 +98,7 @@ Board Documentation
    p201
    p212
    q200
+   radxa-zero
    s400
    sei510
    sei610

doc/board/amlogic/radxa-zero.rst

+.. SPDX-License-Identifier: GPL-2.0+
+
+U-Boot for Radxa Zero
+=====================
+
+Radxa Zero is a small form factor SBC based on the Amlogic S905Y2
+chipset that ships in a number of RAM/eMMC configurations:
+
+Boards with 512MB/1GB LPDDR4 RAM have no eMMC storage and BCM43436
+wireless (2.4GHz b/g/n) while 2GB/4GB boards have 8/16/32/64/128GB
+eMMC storage and BCM4345 wireless (2.4/5GHz a/b/g/n/ac).
+
+- Amlogic S905Y2 quad-core Cortex-A53
+- Mali G31-MP2 GPU
+- HDMI 2.1 output (micro)
+- 1x USB 2.0 port - Type C (OTG)
+- 1x USB 3.0 port - Type C (Host)
+- 1x micro SD Card slot
+- 40 Pin GPIO header
+
+Schematics are available on the manufacturer website:
+
+https://dl.radxa.com/zero/docs/hw/RADAX_ZERO_V13_SCH_20210309.pdf
+
+U-Boot compilation
+------------------
+
+.. code-block:: bash
+
+    $ export CROSS_COMPILE=aarch64-none-elf-
+    $ make radxa-zero_defconfig
+    $ make
+
+Image creation
+--------------
+
+Amlogic does not provide sources for the firmware and for tools needed
+to create the bootloader image, so it is necessary to obtain them from
+git trees published by the board vendor:
+
+.. code-block:: bash
+
+    $ git clone -b radxa-zero-v2021.07 https://github.com/radxa/u-boot.git
+    $ git clone https://github.com/radxa/fip.git
+
+    $ sudo apt-get install -y gcc-aarch64-linux-gnu device-tree-compiler libncurses5 libncurses5-dev
+    $ sudo apt-get install -y bc python dosfstools flex build-essential libssl-dev mtools
+
+    $ wget https://developer.arm.com/-/media/Files/downloads/gnu-a/10.3-2021.07/binrel/gcc-arm-10.3-2021.07-x86_64-aarch64-none-elf.tar.xz
+    $ sudo tar xvf gcc-arm-10.3-2021.07-x86_64-aarch64-none-elf.tar.xz -C /opt
+
+    $ export CROSS_COMPILE=/opt/gcc-arm-10.2-2020.11-x86_64-aarch64-none-elf/bin/aarch64-none-elf-
+    $ export ARCH=arm
+    $ cd u-boot
+    $ make radxa-zero_defconfig
+    $ make
+
+    $ cp u-boot.bin ../fip/radxa-zero/bl33.bin
+    $ cd ../fip/radxa-zero
+    $ make
+
+This will generate:
+
+.. code-block:: bash
+
+    $ u-boot.bin u-boot.bin.sd.bin u-boot.bin.usb.bl2 u-boot.bin.usb.tpl
+
+Then write the image to SD with:
+
+.. code-block:: bash
+
+    $ DEV=/dev/your_sd_device
+    $ dd if=fip/u-boot.bin.sd.bin of=$DEV conv=fsync,notrunc bs=512 skip=1 seek=1
+    $ dd if=fip/u-boot.bin.sd.bin of=$DEV conv=fsync,notrunc bs=1 count=444