doc: boards: amlogic: add documentation for Beelink GT1 Ultimate

Add build instructions for the Beelink GT1 Ultimate board.

Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Signed-off-by: Karl Chan <exxxxkc@getgoogleoff.me>
Link: https://lore.kernel.org/r/8760391a-3506-5ac5-8d55-92c23cccff44@yahoo.com
[narmstrong: fixed MAINTAINERS indentation, added doc to index]
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
diff --git a/doc/board/amlogic/beelink-gt1-ultimate.rst b/doc/board/amlogic/beelink-gt1-ultimate.rst
new file mode 100644
index 0000000..a78a1a2
--- /dev/null
+++ b/doc/board/amlogic/beelink-gt1-ultimate.rst
@@ -0,0 +1,110 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+U-Boot for Beelink GT1 Ultimate (S912)
+======================================
+
+Beelink GT1 Ultimate is an Android STB manufactured by Shenzen AZW (Beelink) with the
+following specification:
+
+- 2GB or 3GB DDR3 RAM
+- 32GB eMMC
+- HDMI 2.1 video
+- S/PDIF optical output
+- 10/100/1000 Ethernet
+- AP6356S Wireless (802.11 a/b/g/n/ac, BT 4.2)
+- 3x USB 2.0 ports
+- IR receiver
+- 1x micro SD card slot
+- 1x Power LED (white)
+- 1x Reset button (internal)
+
+The GT1 (non-ultimate) board has QCA9377 WiFi/BT but is otherwise identical and should
+be capable of booting images prepared for the Ultimate box (NB: there are known clones
+of both boxes which may differ in specifications).
+
+Beelink do not provide public schematics, but have been willing to share them with known
+distro developers on request.
+
+U-Boot Compilation
+------------------
+
+.. code-block:: bash
+
+    $ export CROSS_COMPILE=aarch64-none-elf-
+    $ make beelink-gt1-ultimate_defconfig
+    $ make
+
+U-Boot Signing with Pre-Built FIP repo
+--------------------------------------
+
+.. code-block:: bash
+
+    $ git clone https://github.com/LibreELEC/amlogic-boot-fip --depth=1
+    $ cd amlogic-boot-fip
+    $ mkdir my-output-dir
+    $ ./build-fip.sh beelink-gt1 /path/to/u-boot/u-boot.bin my-output-dir
+
+U-Boot Manual Signing
+---------------------
+
+Amlogic does not provide firmware sources or tools needed to create the bootloader image
+and Beelink has not publicly shared the U-Boot sources needed to build the FIP binaries
+for signing. However you can download them from the amlogic-fip-repo.
+
+.. code-block:: bash
+
+    $ git clone https://github.com/LibreELEC/amlogic-boot-fip --depth=1
+    $ cd amlogic-boot-fip/beelink-gt1
+    $ export FIPDIR=$PWD
+
+Go back to the mainline U-Boot source tree then:
+
+.. code-block:: bash
+
+    $ mkdir fip
+    $ cp $FIPDIR/bl2.bin fip/
+    $ cp $FIPDIR/acs.bin fip/
+    $ cp $FIPDIR/bl21.bin fip/
+    $ cp $FIPDIR/bl30.bin fip/
+    $ cp $FIPDIR/bl301.bin fip/
+    $ cp $FIPDIR/bl31.img fip/
+    $ cp u-boot.bin fip/bl33.bin
+
+    $ $FIPDIR/blx_fix.sh \
+              fip/bl30.bin \
+              fip/zero_tmp \
+              fip/bl30_zero.bin \
+              fip/bl301.bin \
+              fip/bl301_zero.bin \
+              fip/bl30_new.bin \
+              bl30
+
+    $ python $FIPDIR/acs_tool.pyc fip/bl2.bin fip/bl2_acs.bin fip/acs.bin 0
+
+    $ $FIPDIR/blx_fix.sh \
+              fip/bl2_acs.bin \
+              fip/zero_tmp \
+              fip/bl2_zero.bin \
+              fip/bl21.bin \
+              fip/bl21_zero.bin \
+              fip/bl2_new.bin \
+              bl2
+
+    $ $FIPDIR/aml_encrypt_gxl --bl3enc --input fip/bl30_new.bin
+    $ $FIPDIR/aml_encrypt_gxl --bl3enc --input fip/bl31.img
+    $ $FIPDIR/aml_encrypt_gxl --bl3enc --input fip/bl33.bin
+    $ $FIPDIR/aml_encrypt_gxl --bl2sig --input fip/bl2_new.bin --output fip/bl2.n.bin.sig
+    $ $FIPDIR/aml_encrypt_gxl --bootmk \
+                              --output fip/u-boot.bin \
+                              --bl2 fip/bl2.n.bin.sig \
+                              --bl30 fip/bl30_new.bin.enc \
+                              --bl31 fip/bl31.img.enc \
+                              --bl33 fip/bl33.bin.enc
+
+Then write U-Boot to SD or eMMC with:
+
+.. code-block:: bash
+
+    $ DEV=/dev/boot_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=440
diff --git a/doc/board/amlogic/index.rst b/doc/board/amlogic/index.rst
index deb7976..66b581c 100644
--- a/doc/board/amlogic/index.rst
+++ b/doc/board/amlogic/index.rst
@@ -90,6 +90,7 @@
    bananapi-m2s
    bananapi-m5
    beelink-gskingx
+   beelink-gt1-ultimate
    beelink-gtking
    beelink-gtkingpro
    jethub-j80